. 53 

313 
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LABORATORY DIRECTIONS 

IN 

GENERAL ZOOLOGY 



By 

WiNTERTON C. Curtis 

PROFESSOR OF ZOOLOGY, UNIVERSITY OF MISSOURI 



September, 1913 



For Sale by the University Co-Operative Store 
Columbia, Missouri 



LABORATORY DIRECTIONS 

IN 

GENERAL ZOOLOGY 



By 

Winterton C. Curtis 

PROFESSOR OF ZOOLOGY, UNIVERSITY OF MISSOURI 



September, 1913 



♦ » 

- 



For Sale by the University Co-Operative Store 
Columbia, Missouri 






Copyright, 1913, by 
Winterton C. Curtis 



PRESS OF 
W. STEPHENS PUBLISHING COMPANY 
COLUMBIA, MISSOURI 



©CI.A363085 



PREFACE 

These notes are the outcome of one mimeographed and two 
printed editions, which have been written for the introductory 
course in zoology at the University of Missouri. The effort 
has been made with each revision to better adapt them to the 
needs of our students and to make corrections where the plan 
of work or the phraseology had proved unsatisfactory. As 
will be evident to any one with experience in work of this 
character, they are unusually full and this will doubtless be 
a matter of criticism by those who believe that the student 
should receive as little help as possible in the simpler parts of 
his laboratory study. The author agrees entirely with this 
contention and it is the very thing he has attempted in the 
writing of these laboratory directions and in the whole organi- 
zation of his work in the teaching of general zoology. With 
this end in view, the work of the course is so planned that some 
laboratory work shall precede any text-book or lecture study 
upon a given form. Where the student begins his study of 
each animal with laboratory observation, it will be found that 
too brief directions result in his being constantly in need of 
help from the instructor. In such a plan of work he needs 
notes which will offer adequate direction and at the same time 
present a carefully studied attempt to make him determine for 
himself all the points which experience shows are made out by 
the better students. If, in addition, the instructors in a labo- 
ratory will try never to answer any question the student can 
be fairly expected to answer for himself, confining their atten- 
tion to setting him right when he is on the wrong track with 
his material or has misunderstood the directions, and will, on 
'the other hand, spend most of their time in explaining the 
broader aspects of the facts the student sees and in responding 
quickly to the kind of questions he asks when doing under- 
standingly the work called for, the author believes that the. 

Ill 



maximum of efficiency in laboratory instruction will be obtained, 
and these notes have gradually developed in conformity with 
this method of instruction. This procedure should, of course, 
not be pushed to the extreme of having all the laboratory work 
come first, because the student should have another chance at 
the material after his lecture and text-book study have given 
him a broader appreciation of what he can see in the labora- 
tory, the ideal plan being to have the latter part of the labo- 
ratory study follow the main portion of the lecture and text- 
book assignments. When this plan is adopted, it has been 
our experience at the University of Missouri that students can 
be trained to work independently with the directions here 
given, while the advantage for lecture and text-book work lies 
in the fact that the student understands much more readily 
what he reads or hears after he has seen something of it at 
first hand. Thus a good deal of time may be saved, particu- 
larly in lectures, which, when they precede any first hand 
knowledge, often labor to explain what could be much better 
seen and mastered by the student without any preliminaries. 
Most of the work has been written de novo for this course 
although the author has made no attempt at originality in 
many of the minor points, which have been accumulated from 
many different sources and sifted out until they represent the 
result of his teaching experience. In the original mimeo- 
graphed edition, the notes on a number of forms were largely 
a modification of the Laboratory Directions in General Zoology 
by Professor E. A. Andrews of the Johns Hopkins University, 
to whom more than to any other one man the author feels 
indebted for his present habits of thought as a laboratory 
teacher. Very little now remains which would connect what 
is here given with the notes by Professor Andrews. In the 
section on the Earthworm, however, there are a number of 
paragraphs which have survived and perhaps a sentence here 
and there in the notes on the Frog, the Unicellular Forms and 
the Hydra. For permission to use these as they stand in the 
present edition, which is copyrighted and placed on general sale, 
I am indebted to Professor Andrews. The greater part of the 
notes were, however, first written and have since been revised 

IV 



directly from the material and may be regarded as an outcome 
of the laboratory teaching of General Zoology at the University 
of Missouri during the past ten years. I have to thank my 
colleagues, George Lefevre, G. W. Tannreuther, and G. S. 
Dodds, and our assistants who, from year to year, have helped 
with each revision to eliminate the most obvious defects in 
phraseology and method. 

Winterton C. Curtis. 
January 1, 1912. 



PREFACE TO THE PRESENT EDITION 

The present edition has been revised in the light of further 
experience at the University of Missouri and of suggestions 
from other institutions in which the directions have been 
used. Some additions have been made with a view to making 
the work more adaptable, particularly in courses where the 
plan for introductory work in zoology includes a somewhat 
wider range of forms. In this connection, the scope of the 
lecture and text-book work in General Zoology as given at 
the University of Missouri may well be stated. The course is 
one for five hours credit during one semester. The schedule 
calls for two lecture periods of one hour and three laboratory 
periods of two hours each, with reasonable latitude for the 
individual instructor in the substitution of quiz or lecture work 
for some of the laboratory periods. The plan of the laboratory 
work in relation to the entire course of study will be under- 
stood by the following outline: 

I. Representative Forms of Animal Life. 

(Studied with reference to their structure, physiolo- 
gical processes and life-cycles and as living animals 
rather than as representatives of a particular phylum). 

(a) The Frog, as a familiar form. 

(b) Unicellular Forms, to illustrate the basic phe- 
nomena of living things. 

(c) The Hydra, as a simple metazoon. 

V 



(d) The Earthworm, Crayfish or Mussel, as a 
complex metazoon of distinctly different or- 
ganization from the more familiar vertebrates. 
Only one of these is usually studied in full as 
outlined. 

II. The Ontogenetic Development of Animals. 

(a) Cell Division, Maturation, etc. 

(b) Cleavage and Formation of the Germ-layers. 

(c) Life-cycle of Amphibia. 

(d) Embryology of Frog and Chick. 

III. Ecology, Behavior, Intelligence, etc. 

(a) The Insects. 

(b) The Parasitic Worms. 

IV. The Classification of Animals and their Phylogenetic 
Development. 

(a) Brief Examination of the Principal Phyla. 

V. Organic Evolution, lectures and demonstrations only. 

These five main topics, of course, receive emphasis through- 
out the work, but they are more extensively developed in con- 
nection with the laboratory matter above indicated. The 
course, therefore, deals with a rather limited list of animals, 
and while the student is given an opportunity to form some 
conception of the more important phyla there is no intention 
of taking him from end to end of the animal kingdom as is 
sometimes done in courses entitled General Zoology. The aim 
is rather to present the fundamental phenomena of living mat- 
ter as illustrated by representative forms of animal life. 

At the request of Professor W. M. Smallwood of Syracuse 
University, notes are added upon the bony fish and the snail. 
These have been placed in an appendix as they do not logically 
belong at any place in the scheme of the course as here out- 
lined. For these notes and for the outline of work upon the 
arteries of the frog, I have to thank Professor Smallwood and 
the staff at Syracuse University. 

Winterton C. Curtis. 
University of Missouri, 

September 1, 1913. 

VI 



CONTENTS 

Introductory Note - 8 

Frog ., 9 

Use of Microscope 25 

Histology of Frog.„ 27 

Unicellular Forms .. 34 

Hydra 42 

Hydroid Colonies 46 

Hydroid Medusa 48 

Earthworm 49 

Crayfish... 57 

Fresh- Water Mussel 67 

Cytology 79 

Cleavage of Echinoderms 81 

Ontogeny of Amphibia 82 

Embryology of Chick 94 

Insects 97 

Planaria 104 

Tape- worms .105 

Fluke-worms .106 

Classification 109 

Appendix (Bony Fish and Pond Snail) 114 



VII 



INTRODUCTORY NOTE FOR THE STUDENT 

Since the proper understanding of any topic studied in the 
laboratory often involves an exact knowledge of the facts 
previously ascertained in lectures, laboratory and text-book, 
the student should make his laboratory work a matter of 
thoughtful study and should attempt to correlate each new 
fact with what he already knows rather than allow this work 
to degenerate into an unthinking manipulation of hands and 
instruments. Drawings are used solely as a means of enforc- 
ing exact observation and recording the results of the same. 
They are without value for zoology save as they show evidence 
of an understanding of the subject matter. While the ideal 
scientific drawing is not without artistic merit, this is a sub- 
ordinate matter when compared with accuracy of detail. A 
figure by an unskilled draftsman often shows more real under- 
standing of the structures involved than one by a person who is 
merely clever with his hands. Neatness is an important item 
because, it tends to enforce the habits of careful work which are 
conducive to the best observation and representation. 

In beginning laboratory work, the student should be guided 
by the following suggestions: Bring to your seat at the begin- 
ning of the period all the instruments and other articles likely 
to be used, thus avoiding unnecessary moving about the room. 
Follow the laboratory directions explicitly, asking for informa- 
tion only when you do not understand or do not find the 
material. Return promptly all slides or specimens not intended 
for your exclusive use. Handle museum and demonstration 
specimens with great care and do not take from the demonstra- 
tion table, without permission, material intended for gen- 
eral use. 

Your co-operation is asked in the attempt to make the lab- 
oratory a quiet and pleasant place of work and in so handling 
its equipment that every one may derive the maximum bene- 
fit therefrom. 

VIII 



THE LEOPARD FROG (RANA PIPIENS) 

PHYLUM, CHORDATA. SUB-PHYLUM, VERTEBRATA. 
CLASS, AMPHIBIA. 

I. EXTERNAL FEATURES 

(a) Examine a freshly killed specimen in a dissecting pan 
and note the general shape and coloration of the body, the soft 
slimy skin, mouth, anus, nostrils and eyes. What is the 
relative development of the eye-lids and of the nictitating 
membrane, a thin fold which can be drawn over the eye? 
Is there an iris and pupil as in your own eye? How does the 
ear-drum or tympanic membrane differ in position from the 
structure of the same name in your own body? 

(b) * Watch live frogs in the laboratory, or better in a pond,, 
noting the modes of locomotion on land and water and any 
characteristic behavior. In a live frog under a bell- jar watch 
the respiratory movements of nostrils, throat and body and 
try to explain how air is forced in and out of the lungs. How 
is the squatting posture adapted for a quick escape from dan- 
ger? If possible watch frogs in the awkward sprawled out 
position assumed when floating near the surface of the water 
and determine whether this is also a good position for a quick 
escape. Note the hump in the back and, by reference to a 
skeleton, the bones which cause this. Study skeletons of frog 
and man and compare, particularly the skull, vertebrae, 
sternum, clavicles, scapulas, pelvis, and bones of the limbs. 
Understand the terms, dorsal, ventral, anterior and posterior, 
cephalic and caudal. 

Exercise I. Place the animal in the pan dorsal side up, 
pinning out the fore and hind limbs with digits spread apart. 
Show the specimen thus prepared to one of the instructors to* 
make sure it is properly arranged, or compare with the one thus 

(9) 



10 The Frog 

pinned out at the centre-table. Have pencils carefully sharp- 
ened. Rule a faint line lengthwise 'in the middle of a sheet of 
drawing paper and, using this to represent the median plane of 
the animal, show the strict bilateral symmetry which the out- 
side exhibits. Draw on a scale of 1 as thus seen from the dorsal 
aspect. Measure all the distances accurately with ruler or 
compasses and show all the parts to which your attention has 
been called in the foregoing section so far as they appear in this 
view. Finish the drawing in simple outlines, without shading, 
as in the figures posted to illustrate this method of drawing. 
Label thoroughly, making index lines with a ruler and arrang- 
ing the lines and the names to which they lead neatly. 

II. THE MOUTH CAVITY 

(a) Open the mouth and feel the bones in the upper and 
lower jaws. How are the teeth distributed? Fine the vo- 
merine teeth near the internal nostrils. Explore the nasal 
passages with a guarded bristle. How do they differ from 
those of man? Posteriorly the mouth narrows down and passes 
into the oesophagus, the diameter of which may be deter- 
mined by probing with the handle of a needle. Press down 
the eyes from without and observe what happens. The frogs 
thus "pull in their eyes" when hiding beneath stones or other 
objects on the bottom. What is the shape and attachment of 
the tongue? On the mid-line of the floor and well back toward 
the oesophagus is an oval area with a slit in the middle, the 
glottis, above and on each side a large pit, the Eustachian 
recess or tube. Compare these features with what you know 
of the human body. In a male frog there are two small holes 
near the angles of the jaws leading into right and left cavities 
known as the buccal sacs. These may be demonstrated by 
inflation with a blow-pipe. 

Exercise 2. Understand these features thoroughly and be 
prepared to show the relative position of the several parts by 
drawing a sagittal section of the head, or making surface views 
of the roof and floor of the mouth cavity. 



The Frog. 11 

III. THE COELOMIC CAVITY 

(a) Place the specimen in a pan ventral side up and fas- 
ten with pins through the limbs. Pick up the skin along the 
ventral mid-line with forceps and cut through the skin only, 
leaving intact the heavier layer of muscles which is separated 
from the skin by an open space. Continue the cut as a median 
longitudinal incision extending from the jaw to the cleft between 
the hind legs. Cut out at right angles to this in the region of 
the fore limbs and again at the posterior termination of the 
cleft. Reflect the flaps thus formed and pin out in this posi- 
tion. The extensive space between skin and muscles is called 
a lymph sinus. Examine the thighs and fore limbs, making 
small cuts through the skin only and exploring with a bristle 
the cavities thus disclosed. Can you find how these lymph 
cavities are separated from one another? Note fine branches 
of blood vessels extending over the skin and large right 
and left vessels which lie along the partition separating the 
ventral abdominal lymph sinus from those on the dorso-lateral 
surfaces. These are the great cutaneous veins. The cutane- 
ous arteries may be found close to them but are not so readily 
distinguishable since they are no longer distended with blood. 
What fact regarding the distribution of veins and arteries do 
you discover upon studying the finer branchings under a hand 
lens? Along the mid-line, in the layer of the muscles, is another 
blood vessel, the anterior abdominal vein. 

(b) With forceps, lift up the muscle layer in the region 
•of this median vein and cut into the body-cavity or coelome, 
being careful not to injure the underlying viscera. Cut along 
the mid-line as far forward as the sternum and then have one 
of the instructors help you remove a portion of this bone. 
Expose the organs dorsal to the sternum by stretching out and 
pinning the fore limbs. Cut out at right angles posteriorly and 
reflect the flaps as in the case of the skin. 

(c) If the specimen has not been dead too long, the heart 
will be still beating. Without injuring the heart, open the 
sac-like pericardium in which it lies and note the ventricle 



12 The Frog. 

which is single and the auricles of which there are two. Lead- 
ing out anteriorly from the ventricle is a large vessel, the 
truncus arteriosus which divides right and left. On lifting ur> 
the posterior end of the ventricle the sinus venosus may be 
seen leading into the right auricle. 

Exercise 3. As in the case of the mouth cavity, be pre- 
pared to represent these points by a simple diagram. 

(d) As the organs lie in place, one can at once recognize 
the liver with its lobes and the coils of the intestine. On the 
observer's right, the stomach comes out from beneath the liver 
and passes into the intestine as it bends sharply forward. 
Between the liver lobes is the gall-bladder. Lift up the liver 
and find the pancreas, lying in the angle made by the stomach 
and the beginning of the intestine. Find the dark red spleen 
among the coils of intestine and beneath the posterior end of 
the stomach. Also find where the small intestine enlarges into- 
the large intestine and the anterior end of the stomach where 
it communicates with the oesophagus. Locate the lungs and 
inflate them through the glottis with a blow-pipe. On the 
dorsal face of the body wall, find the dark red kidneys with 
finger-shaped fat bodies at one end. In a male, the testes 
are a pair of bean-shaped organs attached to the ventral face 
of the kidney. In the female, the ovaries are attached in a 
similar manner, but are larger particularly in the fall and 
winter when the eggs are maturing for the spring breeding 
season. The oviducts are greatly convoluted tubes lateral to 
the kidneys. Rudimentary oviducts are often found in young 
males. 

(e) With the direction of an instructor, remove the diges- 
tive organs from the body by severing the tract across the 
oesophagus and large intestine. Note in so doing the mesen- 
teries and how the blood vessels run through them. The shiny 
membrane which covers these organs and lines the abdominal 
and pericardial cavities is the peritoneum. Understand from 
the lectures and text-book the meaning of the terms visceral 
and somatic layers of peritoneum, and how the mesenteries are 
related to the same. 



The Frog. 13 

(f) To study the removed digestive tract, begin at the 
-posterior end and unravel the intestine by cutting the mesen- 
teries which hold the various coils in place. Stop this process 
before the region of the pancreas is reached and begin to pin 
out in the dissecting dish under water, reflecting the liver lobes 
as in the specimen placed on the center-table. Find the bile- 
duct which enters the intestine about opposite the middle of 
the pancreas, through which it passes on its course from the 
liver and gall-bladder. The term duodenum is applied to the 
region of the intestine where the bile-duct enters. 

Exercise 4. Draw, on a scale of 3, showing the various 
parts of the tract and its appended glands (pancreas and liver). 
Finish as a simple line drawing and label thoroughly with index 
lines, etc., as in Exercise 1. 

(g) With a sharp scalpel, cut the stomach in two trans- 
versely. Examine the cut surfaces and make out the layers 
as follows: peritoneum, muscle layers, sub-mucosa and, 
lining the tract, the mucous membrane. 

(h) Slit the tract lengthwise from rectum to stomach, wash 
out thoroughly and examine under water, noting the character 
of the lining in different regions. Look for the opening of the 
bile duct into the duodenum. 

(i) Cut thin slices of the liver lobes and examine the cut 
surface under water. 

Exercise 5. Make diagrams on a scale of 2 or 3 to illustrate 
these points (g), (h) and (i). 

IV. THE URINO-GENITAL SYSTEM 

(a) The Female Organs. If the specimen is a female you 
have already identified the paired oviducts and ovaries. 
Examine the latter and note how each ovary is swung to the 
back of the body cavity by a membrane, similar to the mesen- 
tery of the gut, but called the mesovarium. Notice the 
spherical eggs of which the organ is composed. Remove both 
the ovaries by cutting along the mesovaria, being careful not 
to destroy the kidneys and fat-bodies. Follow one oviduct 



14 The Frog. 

to its anterior end and find where it opens into the body-cavity - 
Leaving the left oviduct intact, cut away the peritoneum which 
holds its coils in place and without breaking the duct itself get 
an idea of its total length. Identify the urinary bladder and 
the stump of the large intestine and, leaving these intact, find 
the place at its posterior end where each oviduct dilates into a 
thin-walled sac. Notice how this dilatation passes back dorsal 
to the rectum. The eggs become detached from the ovary 
during the breeding season and pass into the openings at the 
anterior ends of the oviducts. In their passage through the 
oviducts they receive their jelly-like membranes. Finally, 
they accumulate in the dilatations at the posterior ends of the 
oviducts in preparation for the act of laying. 

(b) Examine now a skeleton and understand how the large 
intestine is placed with reference to the bones of the pelvis. 
With the aid of an instructor, cut through the pelvis along the 
mid-line, in doing which you must exercise great care not to 
injure the underlying parts. Spread the cleft apart and, within 
the region thus exposed, cut away the peritoneum at either lobe 
of the bladder, and by breaking away the connective tissue free 
the neck of the same down to its entrance into the cloaca or 
terminal region of the alimentary canal. Leave the bladder 
intact and picking up the stump of the large intestine distin- 
guish clearly between this and the two dilatations of the ovi- 
ducts. Dissect the dilatations away from the rectum down to 
their openings into the cloaca and, lifting each dilatation, find 
the underlying ureters or ducts from the kidneys. Follow 
these last to their union with the cloaca. Notice that the urine, 
feces and reproductive products are all passed into the terminal 
portion of the alimentary canal, which is therefore called the 
cloaca. Pass a bristle into the anus and by moving it about 
determine the diameter of this cloacal region. 

(c) Note again the fat-bodies at the head of the kidneys, 
their shape and mode of attachment and the yellow stripe along 
either kidney which is the ad-renal body. 

Exercise 6. Draw this system from a ventral view on a 
scale of 2 or 3, showing the above points and be prepared to* 
make diagrammatic figures of dorsal and lateral aspects. 



The Frog. 15 

(d) Examine the organs of the other sex, as dissected in 
neighboring specimens, and compare with your dissection. 

(e) The Male Organs. If the specimen is a male, note the 
light colored testes and the mesentery-like membrane, the 
mesorchium, which holds each in place against the kidneys. 
Look in the mesorchium for fine ducts, vasa efferentia, which 
convey the sperm from the testes to the kidneys. Note the 
fat-bodies and the adrenal bodies which appear as a yellow 
stripe on either kidney. Cut away the peritoneum which 
holds either lobe of the urinary bladder and, without destroying 
the bladder or large intestine, find the whitish ureters leading 
back from either kidney. Free the bladder from its attachment 
in the median posterior region, leaving its union with the cloaca 
intact. 

(f) Examine a skeleton and understand how the large intes- 
tine is placed with reference to the bones of the pelvis. With 
the aid of an instructor, cut through the pelvis along the mid- 
line, in doing which care must be exercised not to injure the 
underlying parts. Spread the cleft apart and dissect away the 
connective tissue until you can see the neck by which the blad- 
der opens into the cloaca or terminal region of the digestive 
tract. Lift up the large intestine and follow out in the same 
way the ureters or the ducts from the kidneys. Notice that 
the urine, feces and reproductive products are all passed into 
the terminal portion of the alimentary canal which is therefore 
called the cloaca. Pass a bristle into the anus and by moving 
it about determine the diameter of this cloacal region. In the 
frog the seminal fluid passes from the testes into tubules of 
the kidneys and along these until it reaches the ureters and so 
the cloaca and anus. In immature specimens, rudimentary 
structures comparable to the oviducts are often highly devel- 
oped. Later, these degenerate and become the seminal 
vesicles in which the ripe spermatozoa are stored. These 
should be examined in chart figures if not seen in dissection. 

Exercise 7. Draw the dissection, on a scale of 3, showing 
the bladder reflected to one side and the rectum to the other. 

(g) Examine the organs of the other sex, as dissected in 
neighboring specimens, and compare with your dissection. 



16 The Frog. 

V. THE DORSAL REGION OF THE BODY CAVITY 

(a) The Kidneys and Their Blood Vessels. Before begin- 
ning this dissection, remove the heart and lungs in the following 
manner. With strong scissors make a transverse cut through the 
floor of the mouth about midway between the heart and the 
anterior end of the jaws. Lift up the posterior edge of this 
incision and cut backwards on either side dividing the oesopha- 
gus into dorsal and ventral halves. Taking care not to injure 
the lungs, you will thus remove a rectangular piece from the 
floor of the mouth and oesophagus with the heart and lungs 
attached and uninjured. Put this away for future study. 

(b) With forceps, take hold of the peritoneum on the mid- 
line near the head of the kidneys and by gently raising it see 
the extent of the sub-vertebral lymph sinus. If not already- 
opened by the removal of the oviducts, the cavity of the sinus 
should be further exposed by cutting the peritoneum along the 
lateral border. Lifting the kidney of one side, make out the 
large renal portal vein which runs along the outer margin of 
the kidneys, sending off branches, also the dorsal aorta, a large 
artery which lies behind the kidneys and is formed anteriorly 
by the union of two large systemic arteries. Note how and 
where the dorsal aorta gives off smaller arteries. One of these, 
larger than the rest, is located at the junction of the two 
systemics and is the coeliaco-mesenteric which supplies the 
greater part of the digestive tract. 

(c) In following the directions given in this paragraph 
remove the kidneys and their veins, but not the dorsal aorta. 
Cut any of the small branches of the dorsal aorta which pre- 
vent the removal of the kidneys, leaving their stumps long 
enough to be recognizable. Cut the peritoneum where it 
remains attached around the anterior and lateral margins of 
the sinus and cut across the ureters and renal portals behind. 
This will entirely free the kidneys and leave the dorsal aorta 
and the two systemics uninjured and in place. Upon exami- 
nation of the kidneys under water you can now see the single 
out-going vein, post cava, which lies between them on the ven- 



The Frog. 17 

tral side and the two incoming renal portal veins passing along 
the outer margin of either kidney also fine branches from the 
dorsal aorta. 

Exercise 8. Draw the kidney and its blood vessels on a 
scale of 3, showing by arrows the direction of blood flow. 

(d) Continuing with the parts not yet removed, examine 
the dorsal aorta posteriorly and determine the origin and dis- 
tribution of the two iliac arteries. Lift the portion of the 
oesophagus remaining in the specimen and look for blood 
vessels which leave the systemics. What becomes of the 
systemics when followed anteriorly? Remove the roof of the 
oesophagus and mouth far enough forward to see two carotid 
arteries which pass on either side into a foramen of the skull. 
Do these come from the systemics? 

(e) The Spinal Nerves. Note the segmented back-bone 
covered by a shiny connective-tissue. Examine a skeleton 
and see how the back-bone terminates in a peculiar bone the 
urostyle. Note three pairs of large white nerves on either side 
of the dorsal aorta. Close against the body wall and in front 
of these nerves are three smaller pairs which pass diagonally 
backwards. Working on one side only, lift up and trim away 
the muscles and connective tissue until you find one large and 
two small nerves anterior to those just mentioned. In this 
connection, notice the large subclavian arteries which originate 
from the systemics and pass out along the largest of the nerves. 
What part of the body do they supply? The foregoing nine 
pairs of spinal nerves are numbered I to IX from in front 
backwards. There is in addition a very small X nerve which 
will be seen presently. There are connections between nerves 
II and III, which constitute the brachial plexus, and the more 
complicated unions of nerves VII, VIII and IX which form 
the sciatic plexus. 

(f) The Sympathetic System is not difficult to understand, 
although considerable care is necessary in demonstrating to 
one's own satisfaction the various points. To study it success- 
fully the dorsal aorta and the two systemics must still remain 
intact. Begin by taking the dorsal aorta between your forceps 



18 The Frog. 

just where the two systemic arteries unite, lift gently and look 
for two delicate nerve cords running with a wavy outline in the 
connective-tissue a little to the side of either systemic artery. 
These are the two main trunks of the sympathetic system. 
Each consists of a series of connected ganglia and forms an 
unbroken nerve extending along ventral to the pairs of spinal 
nerves and parallel to the long axis of the body. Taking care 
not to pull too hard on the dorsal aorta, look carefully at the 
sympathetic nerve of one side and note that there are short 
transverse nerves, the rami communicantes (singular, ramus 
communicans), connecting it with the successive spinal nerves. 
These rami are most easily recognized in the case of the IV, 
V and VI nerves. In the anterior region, they are represented 
by the fusion of the sympathetic trunk with the ventral face 
of nerves I, II and III. Demonstrate this fusion to your 
satisfaction. Follow the sympathetic system posteriorly and, 
by careful lifting, make out the number of rami going to the 
nerves of the sciatic plexus. In this posterior region there 
will be noted some yellowish swellings of the cord. These are 
the ganglia of the system. How many can you find and how 
are they placed with reference to the rami communicantes 
Examine now the sympathetic cords in the region of spinal 
nerves I, II and III. The ganglia are here represented by 
swellings of the cords where they cross the spinal nerves. 

(g) The ganglia which are opposite nerves IV, V and VI 
are too small for very satisfactory demonstration in gross dis- 
section, but their position is readily ascertained since they lie 
at the points on the cord where the three conspicuous rami take 
their departure. We have therefore discovered a sympathetic 
ganglion and a ramus communicans for each spinal nerve thus 
far examined. A tenth and last ganglion is usually found con- 
nected with the X spinal nerve, but it is very difficult of demon- 
stration and the number of ganglia in the posterior ends of the 
cords is often subject to considerable variation. When the 
aorta is carefully lifted, the stumps of fine nerves will perhaps 
be found here and there passing from the sympathetic trunks in 
a ventral direction, one that is largest and most conspicuous 



The Frog. 19 

passes along side of the coeliaco-mesenteric artery. This is 
the nerve which runs to the solar plexus. For the distribution 
of these branches of the sympathetic system see description 
in your text-book. 

(h) Cut through one of the systemic arteries just above the 
union with its fellow and, reflecting it outward, examine the 
periganglionic glands, large whitish masses which surround the 
exit of the spinal nerves from the vertebral column. Is there 
one for each spinal nerve? Note just where each spinal nerve 
takes its origin. Find the X pair of spinal nerves and com- 
pare the same in your own and other specimens. 

Exercise 9. Construct a diagrammatic drawing to show the 
spinal and sympathetic systems, on a scale of 3 or 4, as seen 
from the ventral or lateral aspect. The back-bone may be 
shown, but the dorsal aorta is better omitted. 

VI. JOINTS AND MUSCLES 

(a) Examine a skeleton to see how the "head" of the femur 
fits into a depression, the acetabulum, of the pelvis; the whole 
forming a "ball and socket" joint. There is a less perfect one 
where the humerus articulates with the pectoral girdle. At the 
elbows and knees examine the nature of the articulating sur- 
faces of " hinge- joints." Your specimen will probably have one 
of the hip joints still intact and this should be examined by 
removing the muscles until the strong capsular ligament, which 
encloses the head of the femur, is found. How is this ligament 
attached to the femur and to the pelvis? Slit open the liga- 
ment and expose the cavity of the synovial capsule. In what 
directions can such a joint work? 

(b) Strip off the skin of one hind limb and find the gastro- 
cnemius, a large muscle constituting most of the "calf" of the 
leg. To what bones are the tendons of its proximal end 
attached? Distally it is continued into the tendo Achillis. 
Where is this in the human body? What movements do the 
contractions of the gastrocnemius produce? This may be 
determined by cutting the muscle in two at its middle and 



20 The Frog. 

pulling on the stumps. Other muscles, which produce move- 
ments of the knee and ankle joints, may be examined to under- 
stand further how motion is produced at a hing-joint. 

(c) If the nerves of the sciatic plexus are followed outwards 
in the hind limb, their distribution to the muscles will be 
observed, particularly one which innervates the gastrocnemius. 
This muscle and nerve are often used for experimental purposes. 

VII. THE CENTRAL NERVOUS SYSTEM 

(a) Pin the specimen down dorsal side up and remove the 
skin from anus to nostrils. Note in so doing the extensive 
lymph sinuses and the rich blood supply of the skin. Anteri- 
orly between the eyes the roof of the skull will be seen. Exam- 
ine a skeleton and see what bones you must cut through to 
expose the brain and spinal cord. It may now be found more 
convenient to cut off both hind limbs close to the trunk and to 
hold the specimen in the palm of the left hand as you remove the 
flesh. Use your scalpel to pare off the muscles until the spinal 
column is exposed, then scrape away the muscles on either side 
of this until you reach the transverse processes of the vertebrae. 
With the vertebral column thus exposed, pare down the tops 
of the vertebrae until the spinal cord is reached. Being very 
careful not to cut into the cord and brain, continue this paring 
process until you can see the entire cord and brain and by 
chipping away on the sides expose the full width of both. In 
doing this you will probably injure more or less the two mem- 
branes which surround the brain and cord. They are, the 
outer and thicker dura mater, and the inner and more delicate 
pia mater. The former lines the vertebral and cranial cavities, 
the latter is the pigmented membrane which closely invests 
the surface of the brain and cord and is in places distended with 
blood vessels. From this point on the dissection should be 
made under water. 

(b) Beginning at the anterior end of the brain find the two 
large olfactory nerves passing forward to the nasal region. The 
olfactory lobes, from which these nerves originate, are not very 



The Frog. 21 

distinctly marked off from the cerebral hemispheres which 
constitute the greater bulk of this anterior region of the brain. 
Next is a narrowed portion, the thalamencephalon, followed by 
the paired optic-lobes and behind these, if it has not been 
destroyed, a dark area formed by a mass of blood vessels in 
the choroid plexus. Pull the choroid plexus free along one side 
and reflect it to show the cerebellum, a transverse ridge, and the 
fourth ventricle, a triangular cavity in the anterior end of the 
ispinal cord. This anterior end of the cord, which increases in 
diameter before it merges into the brain, is the medula oblon- 
gata. If not pulled off with the pia mater, a delicate pro- 
tuberance, the pineal body, may be seen on the mid-line at the 
anterior end of the thalamencephalon. By gently pressing the 
brain aside in the region of the thalamencephalon, find the 
optic nerve which leads from the ventral side of the brain to 
either eye. Another pair of large nerves, the fifth cranial, will 
be found coming off from the brain in the region beneath the 
optic lobes. There are a number of other cranial nerves but 
their dissection is very difficult and you are therefore referred 
to figures in your text-book where their position is shown. 

(c) The ten pairs of spinal nerves, seen on the dorsal sur- 
face of the body cavity, arise from the spinal cord. The 
largest of them can now be made out leaving the cord by dorsal 
and ventral roots. 

Exercise 10. Draw the brain and cord from a dorsal view 
on a scale of 3 showing the parts above made out. Indicate 
by an outline the position of the head, fore-limbs and eyes. 
If the exact outline of the cord is not clear, it may be deter- 
mined after removal as in paragraph (d) below. 

(d) Remove the cord and brain by lifting gently and cut- 
ting the nerves. Place in water and study the lateral and ven- 
tral aspects. Draw if time allows, comparing with figures or 
models of other vertebrate brains. 



22 The Frog. 

VIII. THE LUNGS AND LARYNX 

(a) Examine these organs from the specimen cut out and 
laid aside earlier in the work. Note again the character of the 
glottis. Find the hyoid cartilage in the floor of mouth. Locate 
the larynx and carefully clean off its ventral surface to see 
where the lungs connect with it. Is there a wind-pipe or 
trachea as in the human body? Separate the dissection into 
right and left halves, by a cut passing exactly along the mid- 
line and through the glottis. This is best done by a careful use 
of the scissors. The laryngo-tracheal chamber into which the 
glottis opens is now exposed. Find the vocal cords and the 
opening into either lung. 

Exercise 11. Make a large outline of a frog's head and 
anterior part of body from a side view. Add to this an outline 
of the mouth cavity, the beginning of the oesophagus and the 
larynx and lung as they appear when cut as above. Specimens 
of whole frogs cut in this way may be examined at the centre- 
table. 

IX. PHYSIOLOGICAL EXPERIMENTS 

(a) Gastric Digestion. Clean thoroughly three test-tubes 
and fill each one-half full of distilled water. Put into the first 
3 or 4 drops of hydrochloric acid and a little pepsin, into the 
second the pepsin, but no acid, and leave the third with only 
the water. Put a small amount of some suitable proteid 
material into each test tube and watch the changes during the 
first few hours. Look up text-book and lecture notes on 
gastric digestion. Record the changes taking place in each 
tube. 

(b) Dialysis Experiments. Make a simple dialyser by 
tying a piece of some animal membrane over the end of a wide 
piece of glass tubing. Fill about half full with a solution con- 
taining sugar in distilled water and place in a somewhat larger 
cylindrical vessel. Pour distilled water into the larger vessel 
until the liquid stands at the same level in the two. Set aside 



The Frog. 23 

and after an hour or two taste the water of the outer tube. 
Record the results. 

(c) In place of the salt or sugar solution put some white of 
egg dissolved in water into the inner tube. After it has stood 
for about the same time as the other test the outside water for 
albumen. This may be done by pouring a little into a test 
tube and heating. Note results and then test in same way 
the fluid of the inner tube to which the solution of albumen 
was added. 

(d) Central Nervous System. Follow the demonstrations 
with frogs in which (1) the cerebral hemispheres, (2) the entire 
brain and (3) the spinal cord have been successively destroyed 
and write out your conclusions regarding the functions of the 
various parts of the nervous system, also the importance of 
"intelligent" acts in the frog's daily existence. 

(e) Muscular Action. Follow the demonstrations of the 
gastrocnemius muscle and its nerve and write out your con- 
clusions regarding the nature of nervous control over muscle 
and the stimuli which affect muscle and nerve. After observ- 
ing the action of the heart of a frog or turtle some time removed 
from the body, write out a statement of the meaning of death 
in the light of these facts. 

X. THE HEART AND BLOOD VESSELS 

(a) The course of arteries and veins is more readily traced 
after these vessels have been injected with some colored mass. 
Specimens so prepared may be dissected for the blood vessels 
and at the same time as a review of the organs and systems 
already studied. 

(b) Heart. In a specimen freshly anaesthetized, examine 
the uninjured pericardium and consider what important func- 
tions this may possess. Determine again the main divisions 
of the heart as in (c) on p. 11, and the exact order of their 
contraction. Refer to diagrams of the internal mechanism of 
valves, etc. 



24 The Frog. 

(c) Arteries. Leading away from the ventricle is the 
truncus arteriosus which divides right and left over the ante- 
rior margin of the auricles into two parts. Each of these 
again subdivides into three aortic arches. Of these three, 
the most anterior is the carotid, the middle the systemic and 
the most posterior the pulmo-cutaneous arch. The aortic 
arches subdivide as follows: The carotid arch soon divides 
into the lingual or external carotid and the internal carotid, 
the carotid gland occurring at the point of division. The 
pulmo-cutaneous arch divides almost immediately into the 
pulmonary and the cutaneous. The systemic arch passes 
dorsally and posteriorly, uniting with its fellow to form the 
dorsal aorta, as seen in the earlier dissection. Each systemic 
gives off an oesophageal, an occipito-vertebral and a sub- 
clavian, the last being known as the brachial after it reaches the 
arm and dividing at the elbow into the radial and ulnar. The 
dorsal aorta gives rise to: (1) the coeliaco-mesenteric which 
branches into the coeliac, to stomach and liver, and the mes- 
enteric, to small intestine; (2) the urino-genital arteries; 
(3) the lumbars; (4) the posterior mesenteries. Posteriorly,, 
the dorsal aorta divides to become the common iliacs, from 
which arise the epigastrics and recto-vesicles. In the thigh, 
the common iliac is known as the sciatic and gives off the 
femoral. At the knee the sciatic divides into the peroneal 
and tibial. 

(d) Capillaries. The branches of the three aortic arches 
thus distribute the blood from the heart to all parts of the body 
and end in the network of capillaries. Examine a demonstra- 
tion of the capillary circulation in the web of a frog's foot and 
determine the following points: Where does the pulse die out? 
What is the diameter of these smallest blood vessels as com- 
pared with the diameter of the corpuscles? How would you 
distinguish between arteries and veins? What is the struc- 
tural basis for the interchange of material between the blood 
and the tissues? 

(e) Veins. The dissection of the veins in the frog is of 
greater interest from the standpoint of comparative anatomy 
than along the general lines of physiology desirable in the 



The Microscope 25 

present study and may, therefore, be dispensed with in a course 
of this nature. Particularly as a considerable number of the 
larger veins have already been examined by dissection. These 
isolated portions should now be reviewed and put together by 
the examination of the present specimen and of text-book or 
chart diagrams. In this connection, consider the blood supplies 
of the kidneys and the liver and the meaning of the term 
"portal system." Also the phenomenon of cutaneous respi- 
ration and how the oxygenated and unoxygenated blood occur 
in the veins and arteries. Again, can we speak of "pure" and 
"impure" blood without a further definition of terms? 



THE USE OF THE MICROSCOPE 

I. PARTS OF THE INSTRUMENT 

(a) If you have previously used a microscope and are 
thoroughly familiar with its working, examine carefully the 
instrument assigned to you, noting the peculiarities, and then 
read over this section as a review. Special work will be 
assigned if you are ready to proceed before other members of 
the class who are using the instrument for the first time. 

(b) Examine the parts of the instrument and find out their 
uses and names by the following description: The light from 
the window can be reflected up from a moveable mirror through 
a small hole or diaphragm in the flat plate or stage, upon which 
is to be placed the object to be examined. The observer looks 
through a tube to which the lenses are attached. The cylin- 
drical eye-pieces slide into the top of the tube near the eye. 
The more complex objectives are to be taken from their brass 
boxes and screwed into the lower end of the tube near the 
object. At this lower end there is attached a swinging nose- 
piece to carry both objectives and make the changing from one 
to the other more convenient. The hole in the stage may be 



26 The Microscope. 

made smaller by diaphragms which slip in, or by an iris dia- 
phragm in the more elaborate instruments. 

(c) As the microscopes used in any course may be from 
different makers, you should consult tables posted in the 
laboratory and giving the magnifications with the different 
combinations of lenses in the instrument you are using. Learn 
to recognize, by their numbers and the size of the lenses, the 
"high power" and "low power" eye-pieces and objectives. 
Examine a chart showing the parts of a microscope and how the 
light passes through the lenses. 

(d) Clean thoroughly a glass slide and one of the thin 
cover-glasses by washing in weak alcohol and rubbing dry with 
a piece of cheese-cloth. With a pipette, put a small drop of 
water on the slide and with needles and forceps unravel a few 
hairs of woolen cloth in the drop. Handling the cleaned cover- 
glass with forceps, lower it carefully upon this drop. Place 
the slide thus prepared upon the stage of the microscope and 
direct the light through it. Screw the low power objective into 
the nose-piece and insert an eye-piece in the top of tube. To 
see the object clearly "focus" the lenses by moving the tube 
with its coarse adjustment until the fibres are clearly seen. 
More delicate focusing is obtained by the fine adjustment, a 
horizontal milled screw which is turned to the left (counter 
clockwise) to raise the tube; to the right (clockwise) to lower 
it. Compare the two sides of the mirror and in subsequent 
work see what results are obtained by the use of each side. 

(e) After a few days' work with the instrument, a brief 
practical examination may be expected upon the following 
points: (1) Finding light with mirror, which is most easily 
done by removing the eye-piece and looking down into the tube 
through the low objective. (2) Finding the focal plane of an 
object and determination by focusing of the vertical spacial 
relations of its parts. (3) Adjustment of the diaphragm to 
different powers and objects. (4) Mechanism of the fine 
adjustment. 



Histology. 27 

II. RULES FOR USE OF THE MICROSCOPE 

1. Do not touch the glass of lenses ; if they become dirty ask 
the assistant's aid in cleaning them with lens-paper. 

2. Never unscrew the parts of the eye-pieces or objectives. 

3. Use a low power first — a high power afterwards and only 
when necessary. 

4. Do not use the high objective without a cover-glass over 
the object you have placed on the slide. 

5. Use the high power eye-piece, only after the low one 
has been tried. 

6. Do not leave lenses or mirrors exposed to direct sunlight. 

7. With high powers, use a smaller hole in the diaphragm. 

8. Learn to keep both eyes open when you are looking 
through the microscope. 

9. Put the microscope into its case carefully, using care not 
to jam the mirror and nose-piece against the back of the box. 



HISTOLOGY OF THE FROG 

I. THE BLOOD 

(a) Bring a clean slide, a cover-slip and forceps to the 
centre-table where the instructor will give you a drop of the 
frog's blood. Place the slip upon this at once, lowering it 
with the forceps and examine with the low power of micro- 
scope. The numerous corpuscles will be seen floating in a 
clear fluid, the plasma. 

(b) Examine with the high objective and determine the 
shape of the red corpuscles. As the blood stands look for the 
white corpuscles or leucocytes which are likely to attach them- 
selves to the underside of the cover or the surface of the slide. 
Get a clear idea of the shape of these, then with a piece of oil- 
clay make a model of each kind of corpuscle. Demonstrate the 
model to one of the instructors. 



28 Histology. 

(c) Stain with aceto-carmine or methyl-green in the follow- 
ing way: Using a slide having a fresh drop of blood covered 
with a slip, place a small drop of the stain on the slide near one 
side of the cover so it will be drawn under. This may be aided 
by touching the opposite edge of the cover with a bit of filter 
paper. After a moment or so draw off the stain with filter 
paper, using a drop of salt solution to help rinse away any 
excess. Look for the nucleus in each kind of corpuscle. 

Exercise 1. Make a drawing of each kind of corpuscle. 
Size, about 2 inches in diameter. 

(d) Examine a demonstration of the circulation in the web 
of a frog's foot, observing the flow of the corpuscles in the 
capillaries. Can you tell arteries from veins? Can you see 
the pulse in all the vessels? If the material is available, indi- 
vidual specimens of small fish or tadpoles, anaesthetized with 
chloretone, will be given out for individual study of the cir- 
culation in fins or gills. A drawing should be made, if such 
a preparation is examined. 

II. PAVEMENT EPITHELIUM 

(a) Get from the centre-table a bit of the outer layer of the 
skin which frequently sloughs off from formalin specimens. 
Spread out flat in a drop of water on a slide, cover with a slip 
and look for the polygonal cells and their nuclei. 

Exercise 2. Draw a portion of the skin showing a number 
of these cells. Size, about 1 inch across the cell. 

(b) Understand that this pavement of flattened cells com- 
prises only the outermost layer of the skin which is much 
thicker than this and made up of a variety of epithelial, gland, 
muscle and connective-tissue cells. 

III. CILIATED EPITHELIUM 

(a) Get from the centre-table a bit of mucous membrane 
from the mouth of a recently killed frog. Place on a slide in a 
drop of salt solution and tease into small bits with your needles. 



Histology. 29 

Put on a cover and examine with low and then with high power. 
Look for motion among the smaller particles and find out what 
is causing this. Find an individual cell which is separated out 
and on which you can see the cilia. Look also for the nucleus. 
If it cannot be seen in the fresh cells run in a little methyl- 
green or ace to-carmine. 

Exercise 3. Draw a single cell or better a small group show- 
ing the above. Size, about 1 inch across. 

(b) Observe in the demonstration at the centre-table how 
the cilia act upon small objects placed upon the surface of the 
mouth cavity. 

IV. COLUMNAR EPITHELIUM 

(a) Get from the centre-table a bit of a frog's intestine which 
has been macerated by soaking in 35 per cent alcohol, or some 
other macerating fluid. Place on a slide in a drop of the fluid, 
and holding the piece with your forceps scrape off some of the 
mucous membrane. Discard the muscular portion of the wall 
and tease the bit of mucous membrane into very small particles. 
Put on a cover and examine with the low and then with the 
high power. Find the elongated cells each containing a 
nucleus. Look carefully for any structures in the nucleus. 
Some of them, goblet-cells, have a clear oval mass at one end 
or a space in the cell from which such a mass has been dis- 
charged. This oval mass is a drop of mucus, which was about 
to be secreted into the intestine. 

(b) The nucleus can perhaps be made clearer by staining 
with magenta. 

Exercise 4. Draw several of these cells, including if possible 
a good specimen of a goblet cell. Size, about 2 inches in length. 

V. STRIPED MUSCLE 

(a) Cut from any of the body muscles of a freshly killed 
frog, a very small bit of the muscle substance. Put this in a 
watch-glass half full of salt solution and tease out with needles 



30 Histology. 

until you can see with your eye the fibres of which it is com- 
posed. The fibres will be readily seen and the teasing process 
must be stopped as soon as they come apart. Care must also 
be taken not to crush the individual fibres. Put on a slide 
under a cover slip and examine with the low power. The long 
cylindrical fibres are bound together by connective tissue and 
each fibre shows a distinct transverse striation. There is a 
longitudinal striation which is less distinct. Examine a single 
fibre under the high power and make out the sarcolemma or 
membrane surrounding the fibre, and the numerous nuclei. 
Stain with methyl-green or aceto-carmine if the nuclei are not 
easily seen. 

Exercise 5. Draw a portion of a single fibre showing these 
points. Size, about 1 inch in diameter. 

VI. UNSTRIPED MUSCLE 

(a) This may be obtained from the urinary bladder or from 
the muscular layers of the digestive tract. Get from the 
centre-table a piece of this material which has been properly 
macerated. Tease out thoroughly and put on a cover slip. 
Find the spindle shaped cells. Stain with magenta if the 
nucleus is not readily made out. 

Exercise 6. Draw a typical cell of this sort. Size, about 2 
inches in length. 

VII. CARTILAGE 

(a) Get with the aid of the assistant a thin bit of cartilage 
from the end of the sternum, or cut with a razor a thin section 
from the head of the femur of a freshly killed frog. Put on a 
slide in salt solution, cover with a slip and find the transparent 
homogeneous matrix containing numerous cell-spaces, or 
lacunae, in each of which is a nucleated cell. Observe here 
and there the groups of cells formed by binary fission. Stain 
with methyl-green or aceto-carmine. 

Exercise 7. Draw a small area, showing several cells and the 
other points above noted. Size of cells, about one-half inch 
in diameter. 



Histology. 31 

VIII. CONNECTIVE TISSUE 

(a) Carefully separate two of the muscles of the leg of a 
fresh frog and note the delicate web of connective tissue between 
them. Or, note the fine strands of connective tissue between 
the skin and the muscles of the body wall. With fine forceps 
lift up a small shred of this, snip it off with scissors, and place 
it on a dry slide. Then, with two needles, spread it out into a 
thin layer, breathing on it to prevent drying. Place a cover- 
glass upon the preparation and then let a very small drop of 
salt solution creep under the cover and moisten the tissue. The 
reason for this procedure is that if connective tissue is placed 
in fluid it contracts into a lump, too opaque for examination, 
and cannot be again spread out. 

(b) Examine first with the high and then with the low 
power and note two kinds of fibres, broad crinkly ones the 
white fibres, and narrow branched ones the elastic fibres. 
Scattered among these are nuclei. Stain with methyl green. 

Exercise 8. Draw, showing the above. 

IX. BONE 

(a) Pieces of dried bone, ground to thin sections, will be 
used. In these only the inorganic substance of the bone 
remains, but the extent and distribution of the bone cells is 
shown by the cavities which the cells once occupied. These 
cavities all appear black, because in the grinding of the section 
they become filled with air and dirt. Examination with low 
and high power will show elongated black areas, the lacunae, 
or spaces once occupied by cells, and radiating out from these 
fine black lines the canaliculi, which in life are occupied, in part 
at least, by delicate processes of the bone cells. Compare the 
structure here observed with that seen in cartilage. 

(b) In some bones, the cells are grouped about canals in 
which run blood vessels. These are termed the Haversian 
canals, each of which with its surrounding cells is an Haver- 
sian system. 

Exercise 9. Draw several lacunae and their canaliculi. 
Size, about 1 inch for the length of a lacuna. 



32 Histology. 

X. WALL OF DIGESTIVE TRACT 

(a) The cells comprising the wall of the digestive tract may 
be studied in place by preserving a small section of the tract 
and cutting this into very thin sections. As the process by 
which such objects are made ready for cutting is somewhat 
elaborate, material will be provided already embedded in 
paraffin and will be cut for each student by one of the instruc- 
tors. Or, permanent slides may be used, in which case great 
care should be exercised not to break covers or even to press 
upon them with fingers or objectives. 

(b) If the material is to be cut for each student, clean a 
slide very thoroughly, as this is to be a permanent mount, 
smear on one side toward the middle of the slide, and over an 
area about the size of your cover-slip, a small amount of 
albumen fixative. Allow a drop of distilled water to spread 
evenly over the smeared area. Place the "ribbon" of sections 
on this water and draw off the excess of water with filter paper. 
See that the ribbon is in such a position as to give a neat appear- 
ance and paste a gummed label on one end of the slide. The 
preparation should now be set aside until the water has all 
evaporated, 24 to 48 hours being sufficient if the slide is kept 
in a warm place. 

(c) When all the water has evaporated, place the slide in 
a jar of xylol for several minutes, to dissolve the paraffin, during 
which time a cover-glass may be carefully cleaned. As quickly 
as possible after this, place the slide right side up on a clean 
piece of filter paper. Add a drop of balsam before there is 
time for the xylol to evaporate and then lower the cover glass 
into place with forceps, being careful not to include air bubbles. 
If the cover glass does not have its sides parallel with those 
of the slide, move it into this position so that when the slide 
is permanently dry it will present a neat appearance. Wipe 
off any xylol remaining on either side of the slide and the 
preparation may be studied at once, if care is exercised not to 
press down on the cover with the objectives or otherwise, before 
the balsam has set hard. Even when hard, a similar precau- 



Histology. 33 

tion should always be exercised in handling this or other slides, 
as such preparations represent many hours of work and are 
easily ruined through careless handling. Another precaution 
is the keeping of the slides in a horizontal position as long as 
the balsam is thin enough to flow. This may be for a period 
of several weeks. You should therefore always keep such 
preparations in the regular slide boxes provided for the pur- 
pose and the box on end. 

(d) Examine with low power identifying the layers of 
peritoneum, longitudinal muscle, circular muscle, sub-mucosa, 
and mucosa, comparing them with the figure made from a 
transverse section cut with a scalpel. Studying further with 
low and high objectives, note the peritoneum, which is a pave- 
ment epithelium, here seen edgewise; the layer of longitudinal 
muscles, here with its cells cut transversely; and the circular 
muscles, here cut lengthwise. Recall text-book or lecture 
notes upon the cells of smooth muscle. The sub-mucosa is 
composed of connective tissue, blood vessels, etc. The mu- 
cosa shows typical columnar epithelial cells, some of which 
may be goblet-cells with their drops of mucous. If the stomach 
is being studied the gastric glands will be seen. 

Exercise 10. Make a figure, about 2 by 5 inches, which 
will show a small part of the circumference and all the layers. 
This figure should show not merely the several layers, but also 
the details of their cells as they appear in the section studied 
and should accurately represent what appears in your par- 
ticular preparation. 

XI. SECTIONS OF SKIN 

(a) Sections cut at right angles to the surface of the skin 
may be prepared in the same way as the sections of the digestive 
tract. Examine such a section with low power making out the 
two layers, epidermis and dermis. The dermal portion has 
conspicuous glands. With the high objective, find the layers 
of cells composing the epidermis. Where is the pavement 
epithelium of your previous study? Find how the cavities 



34 Unicellular Forms 

of the glands open to the outside. Are the cells lining the 
glands derivatives of the dermis or the epidermis? What is 
the direction of the connective tissue fibers in the dermis? 
Do you see anything like blood vessels? Note the position of 
any connective tissue nuclei and pigment cells in the dermis. 
Exercise 11. Draw a section of the skin showing the above 
points. The figure should be made at least 3 by 4 inches to 
enable you to show the cells properly and should be drawn 
accurately for the details of your particular section. 



UNICELLULAR FORMS 

Phylum, Protozoa 

I. THE " PROTEUS ANIMALCULE," 
(AMOEBA PROTEUS) 

Amoeba is frequently found in fresh water and is often 
obtained for laboratory study by placing pond plants in a dish 
and allowing them to stand. After such a culture has remained 
undisturbed for several days, the scum which forms on the sur- 
face of the water or against the sides of the dish should be 
examined for amoeba. For this laboratory work, slides of 
such material freshly mounted and known to contain amoeba 
will be given out. 

(a) Use a very small aperture in the diaphragm and look 
with the low power objective for transparent objects having 
much the appearance of extended white blood corpuscles, but 
considerably larger. After finding such an object examine 
under high power and if it is an amoeba you will recognize the 
flowing movements seen in the white corpuscles. 

(b) Watch the changes in shape. Does the animal accom- 
plish a definite locomotion by this means? The processes 
which flow out from the amoeba are called pseudopodia, i. e.,. 
" false feet." 



Unicellular Forms. 35 

Exercise 1. Make four drawings showing the outlines 
assumed by a single amoeba at intervals of one minute. 

Exercise 2. Begin a large drawing of an amoeba by making 
an outline 3 to 4 inches across and add to this the items noted 
in the following sections as you come to them. 

(c) Examine the structure of the substance composing the 
amoeba. There is an outer region of clear ectosarc and an 
inner mass of granular endosarc. Recall the condition in the 
white corpuscles of frog. Some of the larger masses in the 
endosarc will be found surrounded by a vacuole. Sometimes 
the contents of such vacuoles can be recognized as green plant 
cells similar to the ones found living in the water outside; or 
if specimens can be successfully fed on carmine the red particles 
will be found in many of the vacuoles. These spaces are 
vacuoles of digestion or temporary stomachs in which food 
particles are being digested. Examine the various granules 
of the endosarc with a view to determining their size, shape 
and nature. What is the nature of the boundary between 
ectosarc and endosarc? 

(d) A single larger vacuole may be identified as the contrac- 
tile vacuole if it is seen to contract and reappear. 

(e) The nucleus is best made out by looking carefully 
among the vacuoles of a large specimen for an oval mass with 
finely granular transparent contents and about the size of the 
contractile vacuole when expanded. Examine demonstrations 
of stained amoebas. Does the nucleus of the living amoeba 
change its shape? 

(f) If specimens are carefully watched, it is sometimes 
possible to observe the manner in which the food is ingested 
and the fecal matter egested. 

Exercise 3. Complete the large drawing by putting in all 
these details and labeling thoroughly. 

Exercise 4. Study the contractile vacuole as it appears and 
disappears and represent this by diagrams. 

Exercise 5. Study the movements of the cytoplasm by 
which single pseudopodia are formed and withdrawn and repre- 
sent by drawings. 



36 Unicellular Forms. 

Exercise 6. Examine amoebas in a drop of water on a slide, 
but without the cover glass and under the highest magnifica- 
tion obtainable with the low objective. What can you make 
of the third dimension? Correct any errors in your previous 
figures and make a clay model to show the superficial features 
of the amoeba. 

(g) Understand from lectures and text-book what is known 
regarding the life history of the amoeba. 

II. EUGLENA VIRIDIS 

This is another form which frequently occurs in fresh water, 
being some times present in such numbers as to cause the 
green or reddish color in the ooze at the bottom or in the scum 
floating on the surface of ponds and sluggish streams. 

(a) Clean a slide and cover and get a drop of the material 
containing the euglena. With the low power, look for elon- 
gated green bodies which may be at rest or slowly moving about. 
Put one under the high power and observe the form and move- 
ments. Can you distinguish an anterior and a posterior end? 
Look carefully for the structure which causes the locomotion. 
Find specimens which are expanded and others which are con- 
tracted; or better, observe how a single specimen may expand 
and contract. 

Exercise 1. Make a clay model to show the external fea- 
tures. 

Exercise 2. Draw on a large scale, 3 to 4 inches long, the 
outlines of a contracted and of an expanded specimen and as 
you make them out add the following details to the latter draw- 
ing. 

(b) Continue, examining a favorable specimen. Do you 
find anything like a nucleus? Anything like a contractile 
vacuole? What other structures can you find inside or on the 
outer surface? At the anterior end a spot of red pigment will 
be observed. Look at this end for a small notch in the outline 
of the body. This marks the position of the gullet. 

(c) Crush the specimen by pressing on the cover with handle 
of scalpel or needle while you watch with the low power, or you 



Unicellular Forms. 37 

can place your slide on the table, lay a piece of filter paper over 
the cover and press down with finger. Examine a specimen 
thus crushed and see what you can find out regarding the sub- 
stance of which the euglena is composed, i. e., whether fluid or 
solid, granular or homogeneous, etc. 

(d) Prepare another slide and stain with strong iodine or 
methyl-violet. Look for the flagellum at the anterior end and 
add this to the diagram if not already made out. 

Exercise 3. See that your drawing of the expanded speci- 
men contains all the points made out and is thoroughly labeled. 

Exercise 4. Study and draw encysted euglenas if such 
material is available. 

III. THE "SLIPPER ANIMALCULE," (PARAMOE- 
CIUM CAUDATUM) 

When hay or some vegetable debris is soaked in pond water 
for a time a scum collects on the surface and after some days 
numerous moving white specks may appear around the edge 
and at the surface of the dish, often these will be found to be 
paramoecia; or the animals may be found in abundance in 
small stagnant ponds where the water has a foul odor. 

(a) Place a small drop from such a culture on a clean slide. 
Examine first with the low power and without a cover and note 
the rapid movements, characteristic shape and colorless body. 

(b) Put a very small amount of absorbent cotton fibres 
upon the drop of water and then a cover-slip. The animals 
will thus be caught in little pens formed by the meshes of the 
cotton and may be kept within a limited space. Find a speci- 
men which is thus enclosed, but not in any way crushed and 
study with low and high powers. Study the locomotor activ- 
ities. Does the paramoecium act as though it might have 
volition? What determines its movements? 

(c) . What is the shape? How does the anterior end differ 
from the posterior? As the animal becomes quieter make 
out the cilia which cover the surface of the body and cause 
the locomotion, on one side the buccal groove leading into the 



38 Unicellular Forms. 

substance of the body, the contractile-vacuoles, two clear 
vesicles which appear and disappear, food-vacuoles scattered 
through the body and having variously appearing contents. 

Exercise 1. Make a model of the animal to show its exter- 
nal features. 

Exercise 2. Make a drawing, 3 to 4 inches long, showing 
only the outer surface of the body and the cilia. 

Exercise 3. Begin a large sketch, 3 to 4 inches long, showing 
the animal in optical section. Put in all you have thus far 
observed and add other points as you find them. 

(d) Make a fresh mount without cotton and stain with 
methyl-green or aceto-carmine. Look for a nucleus. Does 
the nucleus react differently from the cytoplasm when the stain 
is applied? What do you think the staining indicates regarding 
the chemical or physical composition of nucleus and cytoplasm? 
A smaller micro-nucleus can be demonstrated by more accu- 
rate staining methods. It is embedded in a depression at one 
side of the larger micro-nucleus, which is the one you see, and 
is not likely to be seen by the staining methods here used. 

(e) Look in this preparation for specimens in which many 
stiff processes much longer than the cilia have been extruded 
from the body as a result of contact with the stain. If you do 
not find them try another slide, adding a drop of stain to the 
water on the slide before putting on the cover. These are the 
trichocysts which are used for defensive purposes. 

Exercise 4. Draw, on a large scale, an optical section of a 
small portion of the body margin, showing trichocysts and cilia. 

(f) Take a very small drop of water containing some of the 
animalcules and add an equal amount of water containing finely 
powdered carmine, or India ink. Watch carefully for some 
time and see whether any carmine or ink gets into the body, 
where and how. Study also the action of the locomotor cilia 
as they drive the particles of carmine about. Examine any 
carmine which has entered the body and understand how the 
food vacuoles originate. 

(g) Mount some specimens in a very small drop of water 
and hold in place by the weight of the cover-glass. Study the 



Unicellular Forms. 39 

formation and collapse of the contractile vacuole and time the 
contractions. 

Exercise 5. Write an accurate description, accompanied 
by three drawings, showing stages in the process. 

(h) Put a small drop of water containing paramoecia upon 
a slide and cover with a slip. Draw off the water with filter 
paper until the animals are brought under pressure, but not 
crushed. Examine a specimen with the high power and look 
along the margin of the body for rod-like bodies, the trichocysts 
before discharge. The firm line outside these is the cuticle. 
The trichocysts lie in the region known as the cortex. Draw off 
the water until the animal is crushed and the semi-fluid medul- 
lary region of the protoplasm flows out. Examine this mass 
with your highest power and see what you can make of it. 

Exercise 6. Complete the drawing of an optical section, 
adding as many details as possible. 

Exercise 7. Study and draw stages in binary fission and in 
conjugation if these can be found in any of the cultures. 

IV. PARASITIC PROTOZOA (GREGARINA AND 

MONOCYSTIS) 

Many protozoa live as parasites in the bodies of other ani 
mals. Notable among these, are the gregarines, which occur 
in the digestive tracts of many arthropods. Material for this 
study is readily obtained from the larvae or adults of the 
meal beetle, Tenebrio. 

(a) Take one of the living larvae of the beetle upon a slide 
and cut off the tips of the body, not quite severing the head, so 
that it may be pulled away and the entire digestive tract of 
the animal drawn out. Examine with microscope the contents 
of the tract through its transparent wall without a cover-slip 
and look for individuals which are heavily infected. When 
found, the tract may be chopped or teased to pieces and the 
material distributed on several slides. Or, if the parasites are 
not abundant, each tract may be at once teased and covered 
with a slip. Avoid getting much of the fat-body of the insect 



40 Unicellular Forms. 

mixed with the bits of the digestive tract and do not use salt 
solution unless necessary as the gregarines live longer when in 
the fluid of the gut cavity. 

(b) Look for organisms with sharp outlines and definitely 
divided into two parts, protomerite and deutomerite. Where 
is the nucleus? Is there a cell wall? What is the nature of 
the protoplasmic structure? Do the organisms move and how? 
Do you find more than one type? Are any specimens attached 
in any way? 

Exercise 1. Draw figures of good size representing the 
above. 

(c) Understand the complete life-cycle of such a form, par- 
ticularly the stages of spore formation and conjugation. See 
demonstrations of these stages in Monocystis a parasite from 
the seminal vesicles of the earthworm, and draw if time allows. 

V. YEAST AND BACTERIA 

(a) Clean three test-tubes. Fill the first test-tube two- 
thirds full with distilled water; the second and third two -thirds 
full with Pasteur's solution. To each tube add a little yeast 
culture. Boil the second tube after plugging with cotton. 
Set all three tubes aside in a jar. 

Exercise 1. Observe and record any changes visible to the 
unaided eye in the course of several days. 

(b) Take some of the solution from each test-tube, place on 
a slide covered by a slip and study with microscope. Do you 
find the "yeast plants" in each test-tube? Why? 

(c) Get material from the yeast culture at the centre- 
table. Study and make out the general shape of cells, granu- 
lar content, vacuoles, cell wall, methods of growth and repro- 
duction. Can you find the nucleus? 

Exercise 2. Draw a single cell, size about 1^2 inch in dia- 
meter showing detailed structure and a colony or group of 
cells in outline only. 

(d) Take potatoes that have been in steam sterilizer for one 
hour. Cut in halves with a knife, that has been heated in a 



Unicellular Forms. 41 

flame. Lay halves directly upon the surface of a sterilized glass 
plate, with cut surface upward. Be sure that nothing except 
heated knife touches cut surface. Leave potatoes exposed to 
air of laboratory for one hour, at end of this time cover the 
potato with a sterilized finger bowl. Paste label on glass plate 
and finger bowl with your name and Lab. Section. The 
potato will remain on your table for several days. Each time 
you come into laboratory examine the surface for any changes 
that are visible to the eye. When growths appear scrape off 
a little of the material, dilute with sterile water and examine 
under the microscope. 

Exercise 3. Record the changes from day to day as seen 
with the eye and under microscope. 

(e) Get a small drop of water containing carmine or india 
ink particles and examine under high power; note the motion 
of the smallest specks. This is called "Brownian movement." 
Is it a translation or a vibration? 

(f) Examine a drop of hay or other turbid "infusion" and 
find the cause of the turbidity. Remove the most of the water 
from under the cover and study the objects with a good light 
and high power. Is there any Brownian movement? Is there 
any active translation from place to place? Focus carefully 
and see that each minute body appears light or dark according 
to focus. 

(g) Study a fresh slide and make out what you can as to 
the form and proportions of the different objects. Can you 
make out any nucleus or other internal structure. These 
small objects are Bacteria. What grounds can you give for 
supposing them to be cells? 

Exercise 4. Draw outlines, on a very large scale, showing 
the shapes of as many distinct types as you can make out. 

(h) Examine the various cultures and infusions which are 
on the centre-table and get an idea of the kind of material in 
which bacteria in the active state may be very abundant. 
Do you think they are more widely distributed in their active 
or their resting condition? 

(i) If time allows try to find good cases of "spore forma- 
tion" and of "zooglea." Draw. 



42 The Hydra. 

THE HYDRA. (HYDRA VIRIDIS, OR H. FUSCA.) 

Phylum, Coelenterata. Class, Hydrozoa. 

I. HABITAT AND ACTIVITIES 

The hydra occurs in quiet pools containing leaves and other 
decaying vegetable matter. When such material is brought 
into the laboratory and allowed to stand in a glass jar many of 
the animals will crawl out and attach themselves to the leaves 
and water plants. There occur commonly about Columbia 
two species; Hydra viridis, which is green in color and quite 
small, and H. fusca which is larger and of a brownish tinge. 

(a) Examine jars containing specimens of hydra and note 
whether they tend to collect on the lighter side of the vessel. 
In size they will be found to vary from very short ones up to 
those about one-fourth inch in length. Examine several 
specimens in the jar and see how the free end differs from the 
attached. Are they found in colonies or as individuals? Do 
any have side branches? If such cases of "budding" are not 
found among the living specimens ask for a slide showing this 
condition. The buds are only temporarily attached to the 
parent, each becoming eventually set free and beginning an 
independent life. 

(b) With the aid of the assistant, transfer several with a 
pipette to a clean watch glass containing water from the jar. 
How firmly are they attached? Examine with the eye and 
with a hand lens against the dark background of the table. 
Touch with a needle and note the result. Do any of the 
hydras attach themselves to the glass? 

(c) The process of feeding may be studied next, or it may 
be deferred until the completion of section II below. Take 
an extremely small bit of fresh meat, which you can get by 
teasing out on a slide in a drop of water some lean beef or a 
piece of some fresh-water animal, and with a needle push it 
into contact with the free end of a hydra. If it adheres to 



The Hydra. 43 

the tentacles, examine the specimen under the low power of the 
microscope. If you are unsuccessful with the first after sev- 
eral attempts try other specimens, until you find one that will 
take food. Watch the process carefully. 

Exercise 1. Make several drawings of good size, 2 to 3 
inches long, to show the feeding. 

II. GENERAL EXTERNAL CHARACTERS 

(a) Examine with low power of the compound microscope 
and notice the cylindrical body, which varies much in length 
and is attached at one end. At the opposite end is a conical 
projection, the hypostome, around which are several tentacles. 
How many? The tentacles are covered with knob-like swell- 
ings at intervals varying with the state of contraction. Short 
developing tentacles will sometimes be found. 

(b) The mouth, at the tip end of the hypostome, is round 
when widely open. What shape has it when closed? The 
base of attachment is the thick end by which the animal 
adheres to a support. Sections show that the cells of the base 
are glandular and secrete a sticky substance, by which the 
hydra attaches itself. 

(c) Compare the structure of a bud with that of the parent 
animal. 

(d) Examine now the body of the animal; it is made up of 
a transparent outer portion, the ectoderm, and an inner col- 
ored portion, the entoderm. 

Exercise 2. Make a detailed drawing, 2 to 3 inches long, 
of an expanded specimen to show the above points and an 
outline of a contracted one. 

III. INTERNAL STRUCTURE 

(a) Using a pipette, transfer a specimen to a slide. Put 
on a cover, supported at one side only, by a very small piece 
of clean filter paper which should first be dipped into water. 
Examine with the low and, for the finer points, with the high 



44 The Hydra. 

power. Be careful not to crush. Make out the following" 
points, which can be done most successfully if the specimen 
is well expanded. The transparent ectoderm will be found 
to surround the colored entoderm and the latter to surround 
a central cavity. Look for particles in this cavity. This is- 
the enteron or digestive cavity. Is there anything to indi- 
cate that the tentacles are also hollow? If so, are their cavi- 
ties in free communication with the main enteron? 

(b) Certain clear oval bodies, the nematocysts, are present 
in the ectoderm. In what regions of the body are they found 
and where are they most abundant? 

(c) Projecting into the water near the nematocysts are 
fine hair-like processes, so delicate and transparent they are 
easily overlooked. They are called the cnidocils. 

(d) Remove the bit of filter paper and press gently on the 
cover with a needle until the hydra is crushed, and look for 
large nematocysts with threads projecting from them. Com- 
pare these with some that have not been discharged. Look 
for nematocysts embedded in their cnidoblast cells, and for 
the different types of nematocysts. 

Exercise 3. Draw on a large scale the large barbed type of 
nematocyst, as it appears before and after discharge. Size, 
about 1 inch for diameter of bulb. 

(e) Mount a fresh specimen under a cover and supported 
with filter paper as before and observe the tentacles under 
a low power as aqueous safranin is run under the cover glass. 
See if filaments are discharged and how they look when com- 
pared with the ones seen above. Remove the filter paper 
and with the high power make out the origin of these filaments. 
Understand from your lectures and the text-book the use of 
these organs. Recall the trichocysts of paramoecium. 

Exercise 4. Draw one of the smaller types of nematocyst 
before and after discharge. Size, proportionate to Exercise 3. 

(f) Prepare a fresh slide, supporting the cover with filter 
paper as above, and see if you can discover cell outlines in 
the ectoderm or endoderm of any part of the body. Review 
with this specimen any other points you have in doubt. 



The Hydra. 45 

(g) Study prepared cross-sections of hydra. Note the large 
-central digestive cavity or enteron, also the body wall com- 
posed of ectoderm and endoderm and between them a distinct 
line marking the supporting lamella. 

Exercise 5. Make a diagram of the entire section in out- 
line only to show these facts. Size, 4 to 5 inches. 

(h) Study under the high power and make out nuclei, 
nematocysts, vacuoles, the lines of division between the cells 
and any other details which may be found. 

Exercise 6. Add these details of ectoderm and endoderm 
to a small part of the section shown in Exercise 5. 

(i) The shape of the individual cells will be much better 
understood after studying the macerated specimens. To do 
this, place a hydra on a slide with a very little water, and add 
a drop of Bella-Haller's fluid. After one or two minutes draw 
off the fluid with filter paper and add a drop of strong aqueous 
methyl-violet, which should stand about the same length of 
time. Draw off the stain with filter paper, add a drop of 
water, break up the specimen by a little teasing and put on 
cover glass. Find the several types of cells. If necessary 
separate the masses of cells still further by tapping very gently 
on the cover glass with a needle. The large endoderm, the 
large ectoderm, the interstitial, the gland cells of the endoderm 
and the cnidoblast cells can be made out in the best prepara- 
tions. Understand the position of the interstitial cells and their 
relation to the cnidoblast cells. 

Exercise 7. Draw a typical cell of each kind made out. 

IV. SEXUAL REPRODUCTION 

If specimens are available, study live individuals having 
male and female organs and make drawings, also sections 
showing eggs or young embryos in the ovaries and the testes 
containing spermatozoa. 



46 Hydroid Colonies. 

V. GENERAL POINTS 

Keep hydras for some days in a tumbler, or bottle, near a. 
window and with water fleas or other forms upon which they 
may feed. Watch the process of catching and eating the 
living prey. Watch hydras that are budding and see if the 
buds separate and form new individuals. Get some way of 
marking on the outside of the dish the place of the hydra's, 
attachment and see whether it changes from day to day. Cut 
several hydras into pieces and see if there is "regeneration." 
In making this last experiment use a watch-glass which has 
been thoroughly cleaned and cover with another, or a larger 
glass dish. 



HYDROID COLONIES 
(OBELI A GENICULATA AND PENNARIA TIARELLA) 

Hydroids are marine animals closely resembling hydra in 
their plan of structure. Budding occurs extensively and the 
buds instead of dropping off remain connected with the parent 
stem, forming a colony. In many hydroid colonies there is 
a "physiological division of labor" between the units of the 
colony so that some become nutritive and others reproductive 
individuals. For the study outlined below specimens pre- 
served in formalin will be used. 

(a) Examine museum specimens of Obelia geniculata to 
determine the extent, attachment and mode of vertical and 
horizontal growth of the colony. Examine several of the 
vertical portions in a watch-glass of water with lens or low power 
and note general resemblance to a budded hydra. 

Exercise 1. Draw, on a scale of 2 or 3, a single one of these 
vertical parts, showing how it arises from a horizontal stem. 
So small a figure cannot, of course, show the details and is 
to show only the main parts of the colony and manner of 
branching. 



Hydroid Colonies. 47 

(b) Mount one or more of these vertical parts on a slide 
in a drop of water, selecting with aid of an instructor one 
which has formed its reproductive units. See that the speci- 
men is properly expanded before putting on the cover, and 
support the cover at one side with a bit of filter paper. Notice 
under low power the mode of branching and the individuals 
of the colony, polyps, at the ends of the branches. Do you 
find developing polyps or buds? Compare a single polyp 
with a single hydra, noting mouth, hypostome, tentacles, ecto- 
derm, endoderm and enteron. Each polyp is surrounded by a cup 
formed from an extension of the transparent perisarc which cov- 
ers the stem of the colony. Are there any modifications of the 
perisarc which would make it more flexible? The core of living 
material within the perisarc is called the coenosarc. Can you 
find any indication of ectoderm, endoderm and enteron in the 
coenosarc of the stem? With what part of a hydra is the stem 
comparable? How does food pass to a growing bud, or to the 
horizontal extensions of the colony? The type of individual 
most numerous in the colony and found toward the free ends 
is the vegetative or feeding unit and known as a hydranth. 

Exercise 2. Draw, on a large scale, a single hydranth show- 
ing its connection with the main stem. 

(c) Near the bases of the vertical stems are the reproduc- 
tive polyps, the blastostyles and medusae. The former have 
large cups of perisarc with a small opening at the free end, 
and their core is a continuation of the coenosarc. They are 
comparable to polyps without mouths and tentacles. They 
produce, by budding, the peculiar polyps known as the me- 
dusae. These medusae become detached, much as do the 
buds of a hydra, as soon as they are fully formed and, pass- 
ing through the small opening at the end of the cup, swim away 
in the water. Examine a demonstration of these medusae of 
obelia. There are therefore three kinds of units in this col- 
ony, all formed by budding: (1) Feeding polyps or hydranths, 
(2) blastostyles and (3) medusae. 

Exercise 3. Draw a single blastostyle showing its connec- 
tion with the main stem, as in Exercise 2, and medusae in 
different stages. 



48 A Hydroid Medusa. 

(d) Examine museum specimens of other hydroid colonies, 
noting general shape and appearance, as determined by size 
of the hydranths and nature of the perisarc. For detailed 
comparative study, the hydroid Pennaria tiarella may be used. 
Examine a branch of the colony in a watch glass with lens and 
low power of microscope. How and where does budding 
occur? How do the hydranths differ from those of obelia? 
What is the relation of the ectoderm and endoderm in the 
tentacles? Where are the medusae buds? How many kinds 
of units are present in the pennaria colony when compared 
with the obelia as explained in paragraph (c) ? Compare these 
two hydroids point by point and determine the relative amount 
of specialization which the parts exhibit. On the whole, which 
species would you consider the more highly organized? 



A HYDROID MEDUSA (GONIONEMUS MURBACHII) 

Since the medusae of obelia are very small we shall examine 
a larger form, Gonionemus murbachii, which originates from 
a hydroid colony* in a similar manner. 

(a) Examine a specimen in a watch-glass under water. 
Notice the numerous tentacles, the shape like a flat bell with 
a clapper, the hypostome, and a shelf, the velum, projecting in 
from the margin. The mouth is at the end of the hypostome. 
We speak of oral and aboral sides, not of ventral and dorsal. 
Protruding upon the concave oral surface are four convoluted 
ridges, the reproductive organs, from which the eggs and 
sperm are shed directly into the water. On the oral surface 
above each reproductive organ is a radial canal, extending 
from the central stomach to a circumferential canal at the 
bases of the tentacles. These canals are a modification of the 
simple enteron of an early stage in the medusa's development. 
Each tentacle has a core of endoderm arising from the circum- 

*The life-cycle of gonionemus is not completely known, but a period of 
budding comparable to the hydroid phase of obelia seems to occur. 



The Earthworm. 49 

ferential canal and is covered with ectoderm, as is the entire 
outer surface of the animal. At the base of each tentacle is 
a colored eye spot. Examine the specimen in the watch-glass 
from the aboral side under low power, looking along the cir- 
cumferential canal for clear vesicles, the lithocysts or organs 
of equilibration, and for small developing tentacles. 

Exercise 1. Draw the medusa from an oral view. Size 
about 3 to 4 inches across bell. 

Exercise 2. Draw a vertical section in the plane of the 
radial canals. Size the same as in Exercise 1. 

(b) Much of the above can be understood completely only 
in connection with the explanations in lectures and text-book. 
Understand from these the structure of the medusa as com- 
pared with the hydranth, and the "alternation of generations" 
by which the medusa produces the hydroid colony and the 
colony the medusa. 



THE EARTHWORM (LUMBRICUS HERCULES) 

Phylum, Annulata. Class, Oligochaeta 

I. THE LIVING ANIMAL 

(a) Place a vigorous, active worm upon wet filter paper 
in a dissecting pan and carefully observe the mode of locomo- 
tion. How does it elongate and contract? Can you see stiff 
spines projecting from the sides? Can they be drawn in? Is 
there a rhythm in these changes? Draw the worm through 
the fingers and feel the spines, or setae. How many are there 
on one ring? Place the worm on its back. Does it right itself? 
Will it crawl backwards? Compare the anterior and posterior 
ends, the dorsal and ventral, the right and left sides. Which 
are alike? Touch various parts of the worm to see which 
seem the most sensitive. Note the movements of the soft lobe 
above the mouth, the prostomium. On the mid-dorsal line 



50 The Earthworm. 

look for the blood vessel which shows through the skin. Does 
it pulsate? Which way does the blood move? Hold up the 
worm to the light and see the dark central axis which is the 
digestive tract with its contents. On the ventral side may be 
seen light colored swollen areas, the skin glands. Those on 
some segments may be associated with a smooth swollen band 
passing around the animal, the clitellum. On the 15th seg- 
ment, swellings mark out transverse slits on each side, the 
openings of the vasa deferentia or ducts for the discharge of 
sperm. On the 14th segment in a similar position are the two 
very small openings of the oviducts. Count the entire number 
of segments or somites and record result, comparing with 
counts in neighboring specimens. 

Exercise 1. Draw the anterior end, as far back as a point 
just behind the clitellum, on a scale of 2 or 3 and from a ven- 
tral or a side view. 

Exercise 2. Draw the posterior end on same scale, showing 
about 10 or 12 segments and from a ventral view. 

II. GENERAL INTERNAL STRUCTURE 

(a) For this, study a freshly killed or a preserved worm. 
Fasten down in a dissecting pan, dorsal side up, by pinning 
through the first somite and again toward the posterior end. 
Make an incision about one and one-half inches long, just 
back of the clitellum and on the mid-dorsal line, but do not 
cut too deep. Using fine scissors cut toward the head end 
with great care not to cut deeper than the wall of body and to 
keep on the dorsal mid-line. Spread out the edges of the cut 
body wall and pin them apart after breaking the transverse 
partitions, septa, which connect the inner face of the wall and 
the outer surface of the gut. Slant the pins outward to give 
room for fingers and instruments in working. 

(b) You will now be able to see the brownish intestine and 
on its upper surface the large dorsal blood vessel. Toward 
the head, the gut becomes differentiated and is partly hidden 
by other organs which will be indicated presently. The skin 



The Earthworm. 51 

is made of two layers, the outer, colored part is the real skin, 
the white inner part is the muscle; both together form the 
body wall. Between the body wall and the digestive tract is 
a space, the body cavity or coelom. Thin lines pass from the 
digestive tract to the body wall across the body cavity. With 
a hand lens and a needle one may see and feel that these are 
the partitions, or septa, dividing the body cavity into cham- 
bers one behind the other. What is the relative position of 
septa and external rings? 

(c) Continue the cut forward through the second anterior 
ring. Carefully separate the edges of the cut and see the dif- 
ferent regions of the digestive tract. Identify the following: 
pharynx, oesophagus, crop, gizzard, and stomach-intestine. 
In the sexually ripe animal there are large yellowish-white 
lobes on certain rings; these are the three pairs of seminal 
vesicles. They more or less hide the oesophageal region of 
the digestive tract. There are five pairs of large lateral blood 
vessels, the hearts, which in the living animal may be seen to 
pulsate. On top of the digestive tract in segment 3 is a small 
white body, the brain. Spread out the body wall right and 
left and pin it to the wax, slanting the pins obliquely outward 
as before. In doing this break or cut some of the septa with 
a needle or scissors. How do the anterior septa differ from 
the others? Have they any different use? In all but a few 
of the anterior chambers of the body cavity there are paired 
fluffy masses on each side. These are the nephridia or excre- 
tory organs. With a lens look for fine blood vessels on these 
organs. Turning a part of the intestine to one side you may 
see these fine vessels connected with a median ventral vessel. 
Beneath the median ventral vessel is a large band, the nerve- 
cord. Cut the specimen open for its entire length and care- 
fully separate the various organs to see them more clearly. 
Which segments are differentiated? Which ones merely 
repetitions of similar organs? 

Exercise 3. Make a full page diagram of the region from 
prostomium to beginning of stomach-intestine to show all the 
organs thus far made out. The length of the segments may 



52 The Earthworm. 

be exaggerated and the organs drawn as if separated by dis- 
section. 

(d) Lift up the oesophagus with forceps, carefully cutting 
its attachment to the septa. Cut it across near the pharynx 
and pull it gently back, while cutting off the septa. How are 
the seminal vesicles placed with reference to the gut? Be 
careful not to remove the seminal vesicles from the worm while 
continuing to pull back the digestive tract and to cut the 
septa. Continue this as far back as the beginning of the stom- 
ach-intestine and so lift up and remove from the worm the 
oesophagus, crop, gizzard and part of the intestine in one piece. 
Examine this removed portion of the tract under water and 
correct any errors in your previous drawing. Find the cal- 
ciferous glands, three pairs of lateral pouches on the oesopha- 
gus in the region hidden by the seminal vesicles. Cut open 
lengthwise, wash out and note the character of the lining and 
contents in each region of the tract. If a preserved specimen 
has been used, set aside the undissected portion for the sub- 
sequent work. 

III. COELOME AND NEPHRIDIA 

(a) Clean a slide and cover and, with the aid of an instructor, 
draw out a drop of the coelomic fluid by means of a capillary 
pipette. Place immediately upon the slide, adding salt solution 
if necessary, and examine under high power. Find the white 
corpuscles. What are their characteristic activities? What 
organism do they resemble? Have they nuclei? 

Exrcise 4. Draw, showing characteristic shapes. Size, 
1 to 2e inches across cell. 

(b) Using the preserved specimen dissected under Section 
II, cut out with fine scissors part of a septum with nephridium 
attached and examine under low and high power. The ne- 
phridium is a convoluted tube with interlacing blood vessels. 
In the larger muscular part there may be parasitic worms. 
Look for the ciliated funnel, or nephrostome. Understand 
the function and manner of action of the nephridium. With 



The Earthworm. 53 

the aid of an instructor, obtain a bit of a living nephridium, 
or better, one that is complete. Look for the peculiar flick- 
ering movement of the cilia within the tubule and study this 
with the high power. 

Exercise 5. Draw the nephridium in whole or in part as 
observed. 

IV. THE REPRODUCTIVE ORGANS 

(a) Using the specimen dissected in Section II, wash off 
the region of the reproductive organs by gentle currents from 
a pipette and examine the posterior face of the septum between 
segments 12 and 13. Under a hand lens the two ovaries may 
be seen lying one on either side and near the nerve-cord. Im- 
mediately behind each ovary is an oviduct, seen as a whitish 
area on the front face of the septum between segments 13 and 
14, and in segment 14 as a fine cord which is very short and 
passes diagonally outward to its place of exit on the ventral 
body wall. Locate these parts without much pulling away of 
the remains of septa and nephridia and then make them more 
clear by gently pulling or cutting any tissue which renders 
them obscure. Examine a model and understand how the 
eggs pass from ovary to oviducts. 

(b) Examination of the seminal vesicles, which should 
still be uninjured, will show that the three lobes which extend 
up on either side of the oesophagus are united by a common 
median region which lies below the gut and against the ven- 
tral body wall. A little picking away of this middle region 
will disclose four large bodies, rather indistinct in outline, 
but different in texture from the vesicles and resembling 
crumpled bits of paper. These are really greatly modified 
funnels which lie at the beginning of the male ducts, or vasa 
deferentia. Looking on the ventral body wall and outside 
the seminal vesicles, it is possible to find a fine duct running 
out laterally from the region of each funnel. The two on a 
side unite and pass straight back to the opening of the vas 
deferens on segment 15. By means of these funnels and ducts 



54 The Earthworm. 

the sperms pass out of the seminal vesicles. The sperm fun- 
nels really open within the closed cavity of the seminal ves- 
icles. The sperms originate from bodies somewhat similar 
to the ovaries and in the same relative position in segments 
10 and 11. Although these bodies, which are the true testes, 
are immediately in front of the sperm funnels, the sperms 
upon dropping from the testes do not at once enter the fun- 
nels, but pass up into the lobes of the seminal vesicles where 
they develop to mature spermatozoa, which are then ready 
to enter the funnels and vasa deferentia and so pass to the 
outside. The four testes and the four funnels have there- 
fore a relation to the coelome similar to the ovaries and their 
oviducts, while the seminal vesicles by enclosing both testes 
and funnels in a common cavity prevent the spermatozoa from 
entering the coelome and furnish a place for their later develop- 
ment. 

(c) The seminal receptacles, which should not be con- 
fused with the seminal vesicles, are small whitish bodies at- 
tached to the ventral body wall on either side in the region 
of segments 9, 10 and 11. They open to the outside only 
and their function is to retain the spermatozoa derived during 
copulation from another worm and which fertilize the eggs 
of this individual. 

Exercise 6. Consult a model, or reference figures of the 
entire system, and then construct a semi-diagrammatic figure 
which will show all these parts. Review their relationships 
by tracing the course of the ova and spermatozoa from their 
origin to the external openings of oviducts and vasa defer- 
entia. 

(d) Carefully cut out one of the ovaries and transfer to 
a slide. Add a drop of glycerine, put on a cover and study 
under the low power. The ova will be seen in various stages 
of development. Where are they most advanced? The 
largest ones show clearly a nucleus and nucleolus. 

Exercise 7. Make a drawing 2 or 3 inches in length show- 
ing the entire ovary. 

(e) Understand from lectures and text-book the function- 
ing of the various parts in copulation and egg laying. Exam- 



The Earthworm. 55 

ine again in a whole worm the clitellum, the markings which 
extend forward from this to the openings of the vasa defer- 
entia and the external openings of the oviducts. 

V. NERVOUS SYSTEM 

(a) Lift the pharynx with forceps and cut off the muscles 
that connect it to the body wall. Trace the connections 
between the brain and the ventral nerve-cord and look for 
nerves from the brain and from the collar-like connectives 
around the oesophagus. Determine the number and place of 
exit of the nerves arising from the ventral cord in the region 
just back of the "collar" and in the body at posterior end. 
Cut across the nerve-cord in the mid-body region and remove 
a bit by tearing out with a quick pull of the forceps. This 
piece may help you determine the number of nerves per seg- 
ment. 

Exercise 8. Make a diagram of the nervous system from 
a dorsal or a lateral view. Scale of 3 or 4. 

VI. TRANSVERSE SECTIONS 

(a) Cut transverse sections of an alcoholic specimen about 
one segment in thickness, using a sharp pair of scissors. Study 
under water with the hand lens and make out the position of 
gut, coelome, nephridia, septa, nerve-cord, blood vessels, etc. 
Can you distinguish the different layers of the body and gut 
walls? Notice the typhlosole, a fold of the dorsal wall of the 
gut. How may it be of importance in digestion and absorp- 
tion? 

Exercise 9. Make a drawing, about three inches across, 
which will show the relative position and thickness of the 
various parts. 

(b) Study the permanently mounted sections of this same 
region. Examine first with the hand lens and then with the 
low power to make out the appearance of the parts in such a 



56 The Earthworm. 

section. Then study the cellular structure of each part with 
the high power. 

(c) In the body wall there are four cellular layers. 1. The 
epidermis, composed of short columnar epithelial cells, some 
of which are gland cells, in various stages of activity. Cov- 
ering the outer surface of all these cells is a continuous mem- 
brane, the cuticle, of non-cellular nature and produced as a 
secretion from the epidermis. 2. A layer of circular muscles, 
here cut lengthwise. Are there nuclei and blood vessels 
among these? 3. The thickest layer is a series of longitudi- 
nal muscles, cut transversely, and so arranged as to have a 
feather-like appearance when the groups of fibres are seen in 
this plane. 4. The innermost layer is the lining of the body 
cavity, or peritoneum, which may show cell outlines and nuclei 
in favorable sections. 

(d) In the intestine there are three chief layers. 1. The 
innermost of elongated, very narrow cells, the mucous mem- 
brane. 2. The outermost, a granular mass that may be 
resolved into a layer of large cells, the chlorogogue cells. 
3. The middle, a narrow band of muscle fibres, both longi- 
tudinal and circular. Are there any blood vessels? Any 
cilia? The typhlosole will again be recognized. What is the 
condition of these three layers in this region of the gut? Blood 
vessels, nephridia and septa cut at various angles may require 
some careful study in your particular section. Try to under- 
stand these parts and why they appear as they do in any one 
section. 

(e) Examine the structures which appear in the coelome and 
interpret them in terms of the organs seen in this region during 
your dissection. 

Exercise 10. Draw on a large scale a narrow section of the 
body wall to show a small portion of each of the foregoing 
and on the same page a similar portion of the intestine to be 
located in the right position relative to the body wall. Add 
anything made out in the coelom. 

(f) Study the nerve cord in the above section and note 
the outer layer containing muscle fibres, the three large clear 



The Crayfish. 57 

dorsal areas or "giant fibres," the fibres of the main mass, and 
the position and structure of the ganglion cells. Understand 
from lectures or text-book the nature of the connections 
between the cells of the nervous system. 

Exercise 11. Make a drawing of the nerve-cord in section, 
about 2 by 3 inches. 



THE CRAYFISH. 

Phylum, Arthropoda. Class, Crustacea 

I. LOCAL SPECIES 

Two species of the genus Cambarus are commonly found in 
this vicinity. C. virilis is the more abundant and is the form 
seen in such numbers in the streams and ponds about Colum- 
bia throughout the open months. C. gracilis, one of the bur- 
rowing crayfish, is seldom found in the open water except dur- 
ing February and March, when the females come from their 
burrows along the banks of creeks and ponds and may be seen in 
in the water with their young. By the latter part of March 
these have returned to their burrows, but the young may still 
be found in the open water until the end of May. The pres- 
ence of C. gracilis during the remainder of the year is however 
much in evidence from the u chimneys ,, which the animal 
builds around the air holes of its burrows. These openings 
are very common in moist ground and are often found at a 
surprising distance away from any body of water. 

II. THE LIVING CRAYFISH 

(a) Watch live crayfish in shallow pans or aquaria and 
study their manner of swimming and walking. How sensitive 
are they to touch? By passing your hand across a short 
distance above the specimen, see if it shows any sign of an 



58 The Crayfish. 

acute sense of sight. Try this again with a specimen out of 
water. Place a specimen on its back in the water or on a 
table and determine the acuteness of its sense of equilibrium. 

(b) Put some carmine in the water and see if you can 
detect any currents flowing in a definite direction in the vicin- 
ity of an animal when it remains quiet for a short time. 
Selecting a small individual, or one having a very clean shell, 
look on the outside of the body just above the great claw and 
and in line with the eye and see if you can detect a flickering 
motion, as though something were moving beneath the semi- 
transparent shell. Recall this observation later when you 
come to study the gill chamber. Keep a specimen out of water 
for a few minutes and note the bubbles which come from the 
front part of the body when it is again placed in the water. 
Do they come from a definite place on the body? You should 
be able to give an intelligent explanation of the facts noted in 
this paragraph after you have studied the gill chambers of 
the animal as outlined in section IV of these notes. 

(c) Observe crayfish as they remain undisturbed in aquaria 
containing stones or other objects. Can you tell what deter- 
mines the particular places which the animals occupy. Drop 
small pieces of fresh meat into these jars and watch the result. 
In some of the jars several small fish may be placed and the 
result watched at this and the next laboratory period. Observe 
crayfish in the large tanks or in nature and note any habits of 
concealment and also their mode of swimming. 

III. GENERAL EXTERNAL FEATURES 

(a) For this study a good sized specimen may be killed with 
some anaesthetic or a preserved specimen may be used. Com- 
pare the anterior and posterior ends, the dorsal and ventral 
and right and left sides. Is there any departure from a strict 
bilateral symmetry? Examine the pairs of limbs from the 
posterior to the anterior end. Is the whole animal covered 
by a dense shell? What parts are moveable? How many 
divisions in the posterior part, so-called abdomen? 



The Crayfish. 59 

Exercise 1. After looking carefully at the proportions of the 
body, draw on a scale of 1 the outline of an ideal cross section 
through the abdomen to show the shape of the dorsal and ven- 
tral parts of the shell and the shape and attachment of the 
paired limbs. Do not actually cut across the specimen, but 
make the figure as it would appear if cut across. 

(b) Find the mouth and anus. Note the round openings 
on the bases of the longest feelers (second antennae), they are 
the openings of the kidney-like green glands. Find on the 
dorsal face of the small first antennae the clear flat areas which 
mark the position of the lithocysts or organs of equilibration. 
Examine the bases of the walking legs for openings; they are 
found on the last pair in the male and on the second from the 
last pair in the female. In the male of C. virilis the two first 
pairs of abdominal appendages are modified to form, when 
pressed together, a copulatory organ along which the sperms 
pass after leaving the male openings. What is the condition 
of the corresponding appendages of the female? Place a male 
and a female side by side and note the difference when they are 
viewed from the dorsal side. The body of the crayfish consists 
of three regions, head, thorax and abdomen. Can you find 
anything on the dorsal side which might indicate the line of 
division between the head and thorax? 

IV. THE GILLS AND GILL-CHAMBERS 

(a) Note how the shell, carapace, extends from the back 
down over the bases of the walking legs. Lift up the free 
ventral edge and see the spongy mass formed by the gills or 
branchiae. Taking care not to injure the gills and using your 
strong scissors, remove the overhanging shell from the left 
side, thus exposing the full extent of the gill cavity, but do not 
cut too far dorsally and injure the organs on that side of the 
body. Cut off the walking legs and large claw, chela, of this 
side a short distance from their insertion. Place the specimen 
under water in a dissecting dish and by floating up and care- 
fully parting the mass of the gills get an idea of what a single 



60 The Crayfish. 

gill is like and where it is attached to the body. Move the 
stumps of the legs and see how the outer gills are related to 
them. How many of these outer gills are there? To what 
appendages are they attached? What effect do you think the 
animal's walking would have upon respiration? What struc- 
ture do you find at the place where you saw the flickering move- 
ment under the shell of the live specimen? Back of this 
"bailer" is another, more delicate, blade which you will identify 
later as the epipodite of the first maxilliped. 

(b) Put together all you know about the gill cavity and its 
contents, the water currents you have seen in the vicinity of a 
quiet animal and explain how the gills are always bathed with 
a constantly changing supply of water. 

(c) These outer gills are called podobranchs. Note the 
significance of the name. Keeping the specimen entirely 
under water and lifting the podobranchs one at a time to be 
sure you do not destroy any of the smaller gills which lie close 
beneath, remove all of the podobranchs by cutting them off 
close to their attachment. Cut one across the middle with 
scissors and examine the section under water with a hand lens. 
You should see the incurrent and excurrent blood vessels cut 
across where they run close together. 

(d) The inner layer of gills is now exposed. Are they 
attached to the feet? There are five pairs and a single one in 
front. Opposite which of the appendages are these gills 
located? They are called the arthrobranchs (joint gills.) 
Note again the significance of the name. 

(e) In the lobster there is another layer of four gills lying 
beneath the arthrobranchs. Because they are attached higher 
up and on the sides of the body these last are termed the 
pleurobranchs (side gills). The common European crayfish 
from which the descriptions in most text-books are taken 
possesses a single pleurobranch, but in the adult of our C 
virilis even this has disappeared. Examine museum specimens 
of the lobster dissected to show the three kinds of gills. 

Exercise 2. Make an outline of the cephalothorax in a side 
view, on a scale of 2. Show the stumps of the appendages and 



The Crayfish. 61 

the places from which podobranchs have been removed. Put in 
all the arthrobranchs and show also the "bailer" and the epi- 
podite above noted. Indicate the course of the water current 
t>y arrows. 

(f) Examine specimens macerated in caustic potash and 
notice the delicate chitinous covering of the gills which has 
survived the maceration. Are the gills inside or outside the 
body? In answering this question imagine how they would 
look in a cross section of the animal in the thoracic region of 
the body. 

V. INTERNAL ANATOMY 

(a) Using a freshly killed specimen, cut with large scissors 
along the dorso-lateral surface on either side of the cephalo- 
thorax, taking care not to injure any of the organs lying imme- 
diately beneath the skeleton. Remove this dorsal part of the 
skeleton from the posterior margin of the thorax to a point 
just back of the eyes. Place the specimen in a dissecting dish 
and having it entirely covered with water identify the follow- 
ing: The tops of the gills, which are exposed where you have 
cut into the gill cavity, are seen on either side. The heart 
which may be still beating lies between these on the mid-line 
in a cavity known as the pericardium. It is soft and spongy 
in its consistency and you should be able to distinguish the 
paired openings, ostia, which lie upon its dorsal surface. How 
many are there? The gastric mill or gizzard lies well to the 
front and is roughly triangular. Note its thin and delicate 
walls and the two transverse bars of harder material, by which 
its walls are strengthened. When the specimen is intact 
muscles pass from each of these bars, or sclerites, to the inner 
face of the dorsal skeleton. Find the remains of these muscles 
•still attached to the shell which you removed, and also to the 
posterior sclerites. If the carapace has not been removed too 
far forward you should be able to see the muscles arising from 
the anterior sclerite and attached to the inner face of the shell 
just behind and between the eyes. These muscles form a part 



62 The Crayfish. 

of the complex system by which the grinding of the gastric 
mill is brought about. Passing through the pericardium are 
large muscles which diverge as they pass forward. If these pull 
on their forward ends as the fixed point, what movement will 
they bring about in the abdomen? You can answer this if you 
understand how the segments of the abdomen are articulated 
to one another. For this see specimens macerated in caustic 
potash. The appearance of the region between the heart and 
gizzard differs with the sex and sexual maturity of the speci- 
men. In a female, with well developed ovaries, these latter 
organs are seen as a bi-lobed mass in front and a median mass 
behind the heart. In a male the testes are less conspicuous, 
but have the same general "Y" shape. In specimens which 
are immature or which have recently shed their eggs or sperms 
the organs are quite inconspicuous and need not be noted for 
the present. The digestive gland which is of a yellowish green 
color in a freshly killed specimen will be easily made out, but 
in specimens with large ovaries it may be crowded almost 
out of sight and only found by pressing aside the latter organs, 
(b) Cut off the tops of the gills, sever the extensor muscles 
of the abdomen at the level of the heart, cut back along either 
side of the abdomen as far as the telson and remove the dorsal 
skeleton of this region. The abdominal extensors will be found 
as two thin bands of muscle lying close under the skeleton. 
They may be taken off with the skeleton, though you should 
be careful not to tear away anything else. The intestine will 
now be seen in the abdominal region along the mid-line. Be- 
neath and to the sides of the intestine are masses of muscle, 
which by their combined action flex the abdomen. Compare 
the bulk of these flexors with that of the extensors. Why 
should there be such a difference in the size and hence the 
power of these muscles? Lying on top of the intestine you will 
perhaps make out a very small transparent thread, the dorsal 
abdominal blood vessel. At the anterior end of the abdomen 
the median portion of the reproductive organs may be found 
or, if these are immature, the posterior ends of the digestive 
glands. 



The Crayfish. 63 

Exercise 3. Make an outline on a scale of 2 or 3, of the 
cephalothorax and abodmen. Put into this the organs as they 
now lie in place. 

(c) Remove the heart and look for ostia on its ventral sur- 
face. Note the "Y" shape of the reproductive organs and find 
their ducts leading to the external openings before noted. 
Remove the reproductive organs, being careful not to injure 
the digestive gland or the intestine. Trim off more of the gills 
and pull away the portions of the abdominal extensors which 
remain in the thorax. Make out the connection of the gizzard 
with the intestine and the antero-posterior extent of the 
digestive glands. Cut in from one side and find the oesopha- 
gus ; it is very short and can be best located by noting again the 
position of the mouth. Trace the intestine to its posterior end, 
cut off close to the anus and carefully free it up to its union 
with the gizzard, also free the digestive glands. Cut across 
the oesophagus and remove the entire digestive tract and its 
appended glands in one piece. Float out in water, and cut off 
the left digestive gland close to the tract. Note the region 
between the gastric mill and the intestine. Open the gizzard 
along the ventral mid-line, find the teeth, work them together 
and see how they grind. 

Exercises 4. Draw a side view from the left, showing the 
tract and the right gland in position and the place where the 
left one opens into the tract. 

(d) To study the Nervous System, carefully remove all 
the muscles and viscera from the abdomen and the ventral 
nerve cord will then be seen lying on the mid-ventral line. 
Notice the ganglia. How many do you count? Notice the 
lateral nerves. How many of these? In the cephalothorax 
the nerve cord is concealed beneath transverse ridges of the 
ventral wall of the shell. Cut these with heavy scissors and* 
expose the nerve cord, beginning at the hinder end of the 
cephalothorax and working forward. How many thoracic 
ganglia do you find? Just back of the oesophagus is the large 
sub-oesophageal ganglion, which is connected with the brain 
by two connectives passing around the oesophagus. The 



64: The Crayfish. 

brain or supra-oesophageal ganglion is just behind the eyes. 
Find the nerves passing from the brain to the eyes and to the 
two pairs of antennae. 

Exercise 5. Draw a figure of the nervous system thus ex- 
posed, showing accurately the number of ganglia made out, 
the segments in which they lie and the number of lateral nerves. 

(e) At the anterior end of the body, near their external 
openings already noted, find the excretory organs or "green 
glands." Show the position and shape of these by a dotted 
outline added to Exercise 3. The thin bladder and underlying 
glandular portion of the organ can be readily distinguished. 
Refer to text book for further details. 

VI. THE APPENDAGES 

(a) For this work use either a fresh or a preserved specimen. 
In drawing take the appendages one at a time from the right 
side of the animal and arrange each in such a way that when 
completed all your figures will have the same orientation. 
This is very important for your correct understanding of the 
homologies between the various appendages. It is also impor- 
tant that the parts of each appendage drawn be completely 
labeled and that smaller ones be drawn on a scale of 2 or 3. 

(b) There are all told 19 pairs of appendages. Beginning 
with the abdomen, count the number of pairs in this region 
of the body and compare them with the number of segments. 
The last pair of these is called the uropods, "tail-feet", the 
others the pleopods or swimmerets. Remove the right appen- 
dage of the fourth abdominal somite by cutting close to the 
body. A basal piece, the protopodite, bears two terminal 
pieces, an inner endopodite and an outer expodite. However 
markedly any of the other appendages may seem to differ from 
this plan of structure, all can be shown to be derived from this 
fundamental plan. The only exception is found in the case of 
the first antennae. 

Exercise 6. Draw the appendage on a scale of 3 placing it 
with the end of attachment upward, the exopod to the right 



The Crayfish. 65 

and the endopod to the left. Use this same orientation in all 
your other drawings of appendages. 

Exercise 7. Remove and draw on a scale of 3 the uropod 
of the right side. Label its parts and orient as in the last. 

(c) Note again the difference in the two anterior pairs of 
abdominal appendages in the two sexes. A study of the em- 
bryology shows that they are all formed by the modification of 
the type above explained. 

(d) The thorax has eight pairs of appendages as follows: 
Four pairs of walking legs or pereiopods, the great claws or 
chelae and three pairs farther forward which will be examined 
presently. Remove the right fourth pereiopod and the right 
chela being sure to get all of the seven and the six parts of which 
they respectively consist. In the pereiopod the two proximal 
parts represent a divided protopod while the remaining five 
are divisions of the endopod. In the embryo an exopod is 
present. The great claws are like the two anterior pairs of 
pereiopods save for the union of two of the divisions. Can you 
find where this has occurred? Note the simple modification by 
which the nipper is formed on the chela. 

Exercise 8. Draw this pereiopod in the same orientation as 
your previous figures and show by a dotted outline the position 
the exopod would have if present. 

(e) In front of the great claws are three pairs of appendages, 
known as the maxillipeds (jaw feet) . The most posterior pair, 
or third maxillipeds, are large and easily recognizable. Before 
removal, the right hand member of this pair should be com- 
pared part by part with the walking leg just examined. It has 
the same parts except that an exopod is present and at one 
point two of the segments have fused to form a single one as 
in the chela. This third maxilliped is a very important append- 
age from the fact that it still has the fundamental plan and so 
can be compared with the simpler abdominal appendages, while 
the structure of its endopod shows how we may interpret the 
adult structure of the walking leg. 

Exercise 9. Draw this appendage oriented in the same way 
as the others, on a scale of 3. 



66 The Crayfish. 

(f) Examine, without removing, the second maxillipeds 
which lie in front of the third. They will be found to have 
parts similar to the latter. They should be removed with 
care not to destroy the first maxillipeds which lie close in front 
of them. Identify, as before without removing, the parts of 
these first maxillipeds. There is a large epipodite which lies 
in the gill chamber just behind the bailer. Protruding toward 
the mid-line are two thin flaps which are an outgrowth from 
the protopod, and at about right angles to these are two other 
projections which are the exopdd and endopod. Which is 
which? 

Exercise 10. Remove the right one and draw on a large 
scale, orienting it properly. 

(g) In front of the first maxillipeds are two pairs of maxillae, 
the parts of which should all be identified before the attempt 
is made to remove either one. The posterior or second max- 
illae, have a four cleft protopodite, a delicate endopod and an 
exopod which is fused with the epipodite so that it looks like 
a forward continuation of the latter. What is the function of 
the fused exopod and epipodite? Before this appendage is 
removed the parts of the first maxilla should be identified. 
This smallest of all the appendages consists of three parts, the 
endopod and a bi-lobed protopod. Which is which? 

Exercise 11. Remove the right second maxilla and draw 
properly oriented and on a large scale. 

Exercise 12. Remove and make a similar figure of the right 
first maxilla. 

(h) The mandibles will now be exposed. Against their 
posterior surfaces are a pair of lobes which are not true append- 
ages. Each mandible consists of a heavy basal portion on 
the median side of which is located the cutting edge which is 
shown by the embryology to be a development of the protopod 
and which is comparable to the more delicate median out- 
growths on the first and second maxillae. The three-jointed 
palp which protrudes from the heavy basal piece has its proxi- 
mal joint formed from the protopod and the other two from 
the endopod. The exopod is wanting in the adult. Where 
would it be if it were present? 



The Mussel. 67 

Exercise 13. Remove and draw the mandible of the right 
side properly oriented and on a scale of 3. 

(i) The second antennae will show, when examined in place 
on the specimen, the typical exopod, endopod and protopod 
and the opening of the green glands. 

Exercise 14. Remove the right one of this pair, orient, and 
draw on a scale of 3 to show these points. 

(j) The first antennae, or antennules as they are sometimes 
called, are the only ones which do not show a real division into 
the three fundamental parts, although their two terminal 
portions would at once suggest the endo- and exopod. Remove 
one and examine more carefully the region of the lithocyst or 
organ of equilibration. 



THE FRESH- WATER MUSSEL 

Phylum, Mollusca. Class, Lamellibranchiata 

I. HABITAT, ACTIVITIES AND EXTERNAL 

FEATURES 

(a) The fresh-water mussels or clams are represented in the 
Mississippi Valley by many genera and by species which are 
numbered in the hundreds. They occur most abundantly 
in running water, but some species are more common in ponds 
and sloughs. For the most part, the species resemble one 
another to such an extent in their general structure that the 
following notes may be used for any one of a number of forms 
likely to be used for laboratory work. If specimens are avail- 
able, examine the shells of several representatives of a single 
genus and compare them with one another and with the species 
in another genus. Try by doing this to get a more concrete 
idea of what is meant by a genus and a species. Of late years 
the shells of these mussels have assumed a considerable com- 



68 The Mussel. 

mercial importance in the manufacture of fresh-water pearl 
buttons and, as a by-product, of the lime grits used for chickens. 
There have thus come into existence common names for all 
the easily recognizable species a few of which are given below. 

Quadrula ebena, the nigger head. 

Q. pustulosa, the warty back. 

Q. metanevra, the maple leaf. 

Lampsilis ligamentinus, the mucket. 

L. anodontoides, the yellow back. 

L. rectus, the black sand shell. 

Symphynota complanata, the hatchet back. 

(b) Before adding the title to any of your figures, the spe- 
cies you have been dissecting should be identified, either by 
consulting a collection of named shells, or with the aid of an 
instructor. 

(c) The points which can be observed by study of the liv- 
ing animals are better appreciated after one becomes familiar 
with a pair of shells. Examine such a pair. They are right 
and left. The hinge is dorsal, the gape the ventral side of the 
animal. "Lines of growth" mark the outer surface. These 
indicate periods of active, alternating with slower growth. 
What is the oldest part of the shell judging by these lines? 
This part is called the umbo. A line drawn through the umbo 
and at right angles to the long axis of the shell will divide it 
into distinctly unequal parts. In all species the smaller of 
these is anterior. Some species show bands of different color 
radiating from the umbos, others have protuberances or ridges 
of various sorts on the shell. Why are shells very commonly 
eroded at the umbos? 

(d) Having thus oriented the shell, note other more detailed 
points. Has the hinge more than one layer? Examine the 
edge of a piece of broken shell showing three layers, the peri- 
ostracum on the outside, the prismatic layer, and the mother 
of pearl. What is their relative thickness? Can you find any 
lines of growth which will give a clue as to how the shell grows 
in thickness? A demonstration of the prismatic layer will be 
found at the centre-table. 



The Mussel. 69 

(e) Inside are teeth which lock tightly when the shells 
are together. What function may these have? Good sized 
markings indicate the places of insertion for the anterior and 
posterior adductor muscles which pull the valves together. 
Since there are no muscles which can pull the shells apart how 
might this be accomplished. Shells specially prepared to 
demonstrate this will be at the centre- table. 

(f) There are other muscle scars considerably smaller, but 
easily recognizable. They mark the insertion of muscles which 
move the foot as will be seen later. They are the posterior 
retractor scar, above the posterior adductor; the anterior 
retractor, which is posterior to the anterior adductor; and the 
protractor, which is a short distance below the anterior retractor. 
Extending from one adductor to the other and parallel to the 
margin of the shell is a marking known as the mantle line. 
This is the so-called "water line," often seen in fresh water 
pearl buttons of the larger sizes. What can you make out at 
the edge of the shell regarding the three shell layers? 

Exercise 1. Draw, on a scale of 1, the outer surface of the 
right valve with its dorsal margin toward top of page. Below 
this the inner surface of the left valve should be represented 
in the same orientation. In beginning the figure, put the right 
valve down on the paper and trace the two outlines about it. 
Show all the points of the foregoing section which can be repre- 
sented. Care is necessary in properly representing the exter- 
nal lines of growth. 

(g) Test for yourself, or by examining the results of a dem- 
onstration at the centre-table, determine the effect of acid 
upon the substance composing the shell and also the effect of a 
strong alkali like caustic potash. Of what is the shell com- 
posed? What reason is there for the fact that heavy shelled 
mussels are abundant only in regions of limestone rock? 

(h) Living mussels should now be studied in large aquaria, 
or in individual dishes with enough sand on the bottom to 
allow the clams to bury themselves readily. Lampsilis sub- 
rostratus, a small pond form, is admirable for this purpose and 
may be examined in a finger bowl. Place the mussel on its 



70 The Mussel. 

side and watch it begin burrowing. The fleshy organ which 
can be protruded from between the antero-ventral margins of 
the shells is the foot. How does the animal make its way 
down into the sand or move about? The fleshy membrane 
exposed between the slightly gaping valves is the mantle. 
In a specimen which lies undisturbed on its side or one which 
is embedded in the sand, can you see openings between the 
right and left sides of the mantle at the posterior end of the 
animal? Are there papillae along these openings or elsewhere 
along the mantle margin? Touch parts of this region very 
gently with a needle and determine its sensitiveness. Can you 
distinguish any difference in the degree of sensitiveness between 
the region of these two openings, or siphons, and the part of 
the mantle near the foot? In a quiet specimen, with the 
siphons well open, watch for currents of water in and out of 
the clam by way of the siphons. The existence of currents 
may be demonstrated by dropping powdered carmine into the 
water near the siphons with a clean pipette, or there may be 
enough silt in the water to show the same thing. There is a 
constant, though gentle, current in one siphon and out the 
other. Which is the inhalent and which the exhalent siphon? 
When the mantle edge is strongly stimulated with the needle 
note how the shells quickly close driving water out through 
both siphons. By examining a number of mussels which have 
been left undisturbed for some days in an aquarium with sand, 
determine the normal positions of the animals in their life on 
the bottom. The water currents are of great importance to 
the animal since in addition to the supply of water for respira- 
tion they bring the entire food supply which consists of the 
micro-organisms living on and near the bottom. How the 
animal acts like a sieve which strains out the water and holds 
the organisms will be explained when the internal organs are 
examined. 

(i) If the dish can be placed in sunlight, test the sensitive- 
ness of the siphonal regions to light by casting a strong shadow 
over this end of a well expanded specimen. 



The Mussel. 71 

Exercise 2. Such points in the foregoing as can be well 
described in writing should be properly incorporated in your 
laboratory book. 

II. EXTERNAL STRUCTURE* 

(a) A specimen preserved in formalin, or one just killed 
should be used for this. As the removal of the shell is not 
easy for a beginner, you should have the aid of an instructor 
for this preliminary step. Remove the right valve and study 
the mussel from this right side as it lies in the other valve. You 
will then have your specimen in the same orientation as the 
drawings of the shell. When the shell has been removed, note 
how the mant»le everywhere conforms to its inner surface. 
There will be no breaks in the mantle unless it has been muti- 
lated in the removal of the shell. Find the ends of the follow- 
ing muscles the scars of which you have already seen upon the 
shell, anterior and posterior adductors, anterior and posterior 
retractors and the protractor. Find the line on the mantle 
which corresponds to the mantle line on the shell. The follow- 
ing internal organs can be more or less definitely recognized 
according to the species or the method by which the specimen 
has been prepared: digestive gland, kidney, Keber's organ, 
and pericardium containing the heart. By consulting a chart 
or blackboard diagram, understand their position even if you 
are not able to locate them at this time in your own specimen. 

Exercise 3. Make a figure of the mussel, as it thus lies in 
the left valve of its shell and seen from the right. The removed 
valve may be wiped dry and the first outline of the drawing 
laid down by tracing around it. 

(b) The space enclosed between the right and left halves 
of the mantle and in which the foot lies, is the mantle cavity. 
Without tearing or cutting, find how the incurrent siphon com- 
municates with this and by lifting up the mantle edge get an 
idea of the foot and the four plate-like gills, which extend from 

*The features of the mantle surface and the organs in the mantle cav- 
ity are really a part of the external surface of the animal. 



72 The Mussel. 

the sides and top of the foot to the region of the siphons. Look 
carefully and see the line along which the outer surface of the 
outer gill and the inner surface of the mantle meet. Find the 
palps, a pair of organs on either side of the foot posterior to the 
anterior adductor muscles and note their attachment to the 
inner surface of the mantle. Remove now the right half of the 
mantle by cutting from the middle of the incurrent siphon 
along a line about one-fourth inch below and parallel to the 
place where the gills and inner face of the mantle meet. At 
the region of the palps care should be taken to leave these 
organs intact. Continue the cut just below the anterior 
adductor muscle and thus expose the organs of the mantle 
cavity. Trim off to a neat outline the cut edge of the mantle, 
without injuring gills or palps. 

Exercise 4. Beginning with an outline made by tracing with 
the right valve, construct a figure to show all of the above 
organs, omitting for the present the structure of the region 
above the cut edge of the mantle and the outline of the cut 
edge itself. 

(c) The structure and function of the organs concerned in 
the water currents should now be studied. By looking into the 
uninjured ex-current siphon the intestine ending in the anus 
will be seen on the posterior face of the adductor muscle. 
Extending beneath this adductor anteriorly, is a cavity into 
which a bristle may be thrust for a considerable distance. 
Being careful not to cut too deep, make an incision at the top 
of the outer gill near the middle of its length and expose a 
cavity running along the top of this gill. By gently probing 
with the bristle, explore this cavity forward and back. How 
does it end in either direction? With the bristle thrust in as 
a guide, cut in either direction and expose this supra-branchial 
cavity from the anterior end of the gill to its opening into the 
cloaca, as the region just within the excurrent siphon is called. 
Trim away the tissue on each side of the cut so that the whole 
diameter of this supra-branchial cavity is readily seen. The 
upper line of the cut edge should be made to pass along the 
lower margin of the posterior adductor and end above the anus, 



The Mussel. 73 

the lower cut edge should pass out to where the two siphonal 
openings meet. The floor of this cavity is cut by a series of 
transverse partitions inter-lamellar junctions separating cavi- 
ties, the water-tubes of the gills. If the gill is not too much 
shrunken you can pass a bristle down any of these water-tubes 
to the ventral edge of the gill where it ends blindly. Making 
a clean cut with the scissors at right angles to the water-tubes, 
remove a piece of the gill and examine the cut edge under water 
with a hand lens. The water-tubes and inter-lamellar junc- 
tions will be seen cut transversely. It is in these water-tubes 
that the young of the clam begin their development and you 
may find the gill distended with embryos. By looking forward 
from beneath the posterior adductor and gently exploring with 
a bristle, you can see that the inner gill of this side and the two 
gills on the other have each a supra-branchial cavity and water- 
tubes as in the gill just examined. How would the four supra- 
branchial cavities be connected with the cloaca if looked at 
from the dorsal side? Sketch a diagram of this system of cavi- 
ties as it would appear if viewed dorsally. 

(d) You should now be able to understand how the water 
current, from which the clam gets its food and oxygen and by 
which its carbon dioxide and other wastes are carried out r 
flows through the gills. Coming in by way of the incurrent 
siphon the water freely bathes the organs of the mantle cavity. 
From here it passes through microscopic openings, the ostia, 
which lead from both inner and outer surfaces of all the gills 
into the water-tubes. Passing upwards in the water-tubes, 
it emerges in the supra-branchial cavities and passing backward 
in these it reaches the outside through the cloaca and exhalent 
siphon. The water which passes out has been strained of its 
micro-organisms which are too large to pass through the ostia 
of the gills. These organisms upon coming in contact with the 
slimy surfaces of the gills, foot or mantle are entangled in the 
mucus and carried by cilia along definite lines which finally 
bring them between the palps and to the mouth which will be 
found anteriorly below the adductor and between the continua- 
tions of the inner and outer palps. 



74 The Mussel. 

(e) Examine under the microscope a bit of tissue cut from 
the gill of a living clam and one from the mantle and make 
out the cilia on these surfaces. The ostia will be demonstrated 
in stained sections of the gill taken in the same plane as the 
rough sections previously made with scissors. Place carmine 
or pieces of cork upon the gills or upon various parts of the 
mantle surface of a living specimen and note the result. 

Exercise 4 (continued). Add to your previous drawing 
these details of the supra-branchial and cloacal cavities, taking 
care to show the cut edges where they occur. Put in arrows 
to show the course of the water currents. 

(f) Why are we justified in speaking of the mantle cavity 
as a part of the external surface of the animal? 

III. INTERNAL STRUCTURE 

(a) The mantle, supra-branchial and cloacal cavities are 
really portions of the outer surface of the mussel and only in 
what follows are we dealing with organs which are internal in 
the same sense as the viscera of a frog or other familiar animal. 

(b) In the region above the gills and in front of the posterior 
adductor is the pericardium. Make a small incision in its 
wall and lifting with forceps cut the wall away exposing the 
heart, consisting of a single median ventricle wrapped about 
the intestine which traverses the pericardium, and of delicate 
right and left auricles which lead from the sides of the peri- 
cardial cavity. These last can probably be better seen if they 
are floated out under water. The dark colored kidney will 
be seen underlying the pericardium. 

Exercise 4 (concluded.) Add to your figure the pericar- 
dium as thus exposed and its contained organs. Show clearly 
the cut edge of its wall. 

(c) Lift up the outer gill and remove by cutting away the 
inner wall of its supra-branchial cavity. Locate the supra- 
branchial cavity of the inner gill and cut into this to expose 
its full length. The dark color of the kidney will probably 
show through the wall of this latter cavity, and well toward 



The Mussel. 75 

the anterior end there will be found against this dark area two 
small openings. They are not as easy to find in some species 
as in others but can usually be located. The dorsal one of 
these openings is the external opening of the kidney of this 
side, the ventral is the opening of the reproductive gland or 
genital pore. On the other side of the foot are similar openings 
for the left side of the body. Note that the opening of the 
kidney is thus into a cavity from which the water flows imme- 
diately to the outside. The eggs upon leaving the genital pore 
are fertilized by sperm which have been shed to the outside 
water from an individual of the opposite sex and entered the 
supra-branchial cavity of the female. After being fertilized 
the eggs fall into the water tubes and there develop as far as 
the larval stage, known as the glochidium. 

(d) Begin at the anal end and dissect the intestine entirely 
free from its union with the upper surface of the posterior 
adductor muscles. Turn the specimen up on the ventral edge 
of its shell so you can look into the pericardium from above and 
by taking hold of the intestine and turning it over anteriorly 
expose the extreme anterior end of the pericardium. Careful 
probing with a fine headed bristle should reveal the opening 
from the pericardium into the kidney. Push the bristle as far 
back as it will go and thrust another finely tipped bristle through 
the external opening of the kidney pushing it back also. Cut- 
ting into the substance of the kidney will now reveal the fact 
that one bristle lies in an upper and thin-walled, the other in a 
dark colored and thick-walled cavity. Near the posterior 
adductor these upper and lower limbs of the kidney unite. 

(e) With the handle of a scalpel scrape the tissue of the 
kidney away from the top of the foot and note the two posterior 
retractors, the ends of which have been previously observed. 
Still using the scalpel handle, free these from the adductor 
muscle and the left one where it attaches to the shell. Can 
you see why they are called retractors of the foot? 

(f) Leaving the intestine intact and attached to the foot 
and visceral mass (the term applied to the part of the body 
which lies above the foot and is softer and less muscular than 



76 The Mussel. 

that organ), continue with the handle of the scalpel and break 
away the attachment of the visceral mass to the shell in the 
region of the teeth, being careful not to injure the mouth. 
Remove this part of the body from the shell leaving the anterior 
adductor behind. 

(g) Before discarding the left valve with the posterior 
adductor attached, look on the ventral surface of this muscle 
for a yellowish body which is the fused right and left visceral 
ganglia of the nervous system. Look for nerves extending 
out from this. The pair of cerebral ganglia will probably also 
be seen upon the ventro-posterior face of the anterior adductor 
mussel. Indicate the position of these ganglia upon your 
general drawing. 

(h) Locate the anterior retractors and the protractors of the 
foot and see why they are so called. Remove the palps and 
any remains of mantle or gills from each side of the visceral 
mass and then with a sharp scalpel split this mass and the foot 
as nearly into right and left halves as possible, leaving the free 
end of the intestine attached to the left half. Examine the 
cut surface of the left half under water and pinned down in a 
pan. The visceral mass will be seen to be composed of a pasty 
mass, made up largely of the reproductive gland, in which the 
coils of the digestive tract are embedded. Follow any of these 
canals which are cut by the section. The flattened oesophagus 
leads upwards to an enlargement of the stomach into which 
the right and left halves of the digestive gland open. The 
following out accurately of the digestive tract in any species 
is a difficult piece of dissection for which a second specimen will 
be supplied if you have additional time. The course of the 
tract should be examined in text-book or chart figures. 

(i) In the soft tissue just above the upper margin of the 
foot and a little distance below the mouth, you will find by 
gentle scraping, if they are not already exposed, the pair of 
pedal ganglia. They are yellowish in color and of firmer 
texture than the tissue in which they are embedded. Nerves 
will be found running out from them. Show in your general 
drawing the position of these within the substance of the vis- 



The Mussel. 77 

ceral mass. Understand from lectures, text-book or charts, 
how the three pairs of ganglia, you have noted, are united by 
paired connectives and what parts of the body their nerves 
supply. If you have time, a specimen will be supplied for a 
special dissection of the ganglia and their connectives. 

IV. THE EMBRYOLOGY AND PARASITISM OF 

THE MUSSEL 

(a) At certain periods of the year the gills of the mussel 
are found distended with the glochidia which have been pre- 
viously referred to. Examine in a watch glass of water some 
of these glochidia just removed from a freshly opened mussel. 
Note the two halves of the shell, the adductor muscle between 
them and certain fine projections, the sensory hairs on the 
inner surface. Are there hooks at any point on the shell? 
Beyond the valves of the shell none of the organs of the adult 
are visible. These embryos are shed from the mussel, by way 
of the out-going water current, and scattered upon the bottom 
where they must come in contact with the fins or gills of a fish 
and fasten themselves there in order to continue their develop- 
ment. After leaving the fish they have developed all the organs 
of the adult in miniature and can begin life on the bottom. 
Watch the glochidia for any movements and record nature 
of same. 

Exercise 5. Draw the glochidium on a large scale, as it 
appears gaping open and also from a lateral view when closed. 
The closure of all the specimens can be easily effected by adding 
a few drops of waste alcohol or of methyl-green. 

(b) Take now a considerable number of living glochidia 
in a finger bowl of clean water and put into this one or two small 
fish. Watch how and where the glochidia attach. If the 
fish do not keep the water sufficiently agitated to prevent the 
glochidia settling to the bottom it must be stirred gently. 
After five or ten minutes take out the fish and put one into an 
aquarium. Kill the other without pressing upon the gills or 
fins and pin it ventral side up in a pan of water. Remove gills, 



78 The Mussel. 

fins and tail and examine with microscope in a watch glass. 
How and where are the glochidia attached? 

Exercise 6. Draw one or more glochidia attached to the 
gill or fin, and on such a scale as to make the larvae about one- 
half inch in diameter. 

(c) Make an estimate of how many glochidia there are on 
this one fish, of how many were produced by the single mussel. 

(d) The fish which were set aside after infection should 
be examined at the next laboratory period and the condition 
of the glochidia with reference to the tissue of the fish deter 
mined; or fish infected 24 to 48 hours previously may be pro 
vided for examination on the same day as the foregoing. 
Record the condition of these glochidia and if you have time 
make figures. 

V. TRANSVERSE SECTIONS 

(a) For a review of many points brought out by the fore- 
going study the examination of sections, cut through a speci- 
men from which the shell has been removed, is valuable. In 
sections from the region of the heart, which are perhaps more 
instructive than any others, the following structures should be 
made out and compared with the conceptions and figures 
already obtained; mantle, foot, gills, supra-branchial, mantle 
and pericardial cavities, kidney, Keber's organ, ventricle^ 
auricles and intestine. How is the shell related to the whole? 
How does the water pass from the mantle cavity to the supra- 
branchial cavities? Where are the water-tubes? 

Exercise 7. Draw such a section on a large scale labeling^ 
all the parts and showing the course of the water by arrows. 

VI. SPECIAL DISSECTIONS 

(a) A second specimen may be used for a review of the 
structures previously dissected and the more complete demon- 
straction of the nervous and digestive systems. Remove the 
shell and mantle of such a specimen, examining again any 



Cytology. 79 

points not previously made clear. Locate the cerebral and 
visceral ganglia without cutting anything but the mantle. By 
careful dissection, follow one of the two nerves, which may be 
seen leading anteriorly from the visceral ganglia, to its union 
with the cerebral ganglia. From these latter, three pairs of 
nerves arise; the pair of cerebro-visceral connectives just dis- 
sected, a pair of mantle nerves, and the cerebro-pedal connec- 
tives. Follow one of the last to its union with the pedal 
ganglia and determine the number of nerves arising from the 
latter. 

Exercise 8. Make a figure of the entire nervous system. 

(b) This same specimen may be used for a dissection of the 
digestive tract. To do this remove the entire animal (includ- 
ing the two adductors) from its shell and pin out under water. 
Begin at the mouth and dissect out the tract to show, oesopha- 
gus, stomach, openings of digestive glands and coils of the 
intestine. These latter must be exposed by removing the side 
of the visceral mass which is uppermost and following with 
care each part of the intestine as it is found. 

Exercise 9. Make a figure of the entire digestive tract. 



CYTOLOGY 

I. MITOSIS 

The finer details of cell division must, of course, be studied 
with the very highest magnifications. The more general 
features may be examined with the high powers ordinarily 
used in a course of this nature. Mitotic or indirect cell divi- 
sion appears to be the common method by which cells divide. 
The amitotic or direct mode of division seems to be of less 
importance and its significance is still a matter of doubt. For 
the study outlined below, sections of growing onion root tips 
or the epithelium of salamander larvae may be used. 



80 Cytology. 

(a) Examine the sections with low power to understand the 
relation of the parts, then with highest powers look for cells in 
different stages of division showing the chromatic material in 
the form of chromosomes. Examine chart or text-book 
diagrams of mitosis and determine which phase of the process 
is represented by each cell found in division. Determine, if 
possible, the number of chromosomes in each cell. 

Exercise 1. Construct six cell outlines for figures showing 
consecutive stages. Then put in the nucleus as you find good 
examples of the several steps in the process. Have the series 
in order when completed, but do not try to find them in this 
order. Rather, take representative cells as found in searching 
over the slide and draw into their proper place in the series. 

(b) The following terms have come into use for designating 
the stages in cell division: 

Prophase. The division and migration of the centrosome 
and formation of the spindle, the assumption by the chro- 
matin of thread-like aggregates which segment into chromo- 
somes and the arrangement of the chromosomes into an 
equatorial plate. 

Metaphase. The lengthwise splitting of the chromosomes. 

Anaphase. The divergence of the chromosomes into the two 
daughter groups, and the division of the cytoplasm. 

Telophase. The appearance of a nuclear membrane in each 
daughter cell and the reconstruction of the nucleus to its typical 
resting condition. 

(c) See that all the structures indicated above are properly 
labeled. Test your understanding of the spacial relations, 
of parts by seeing whether you can readily interpret sections 
cut at irregular angles. 

II. MATURATION 

(a) Demonstrations may be examined showing: (1) polar 
bodies in superficial view and (2) the reduction divisions of 
the oocytes and spermatocytes in sections. Understand the 
relation of this process and of fertilization to the number of 
chromosomes and its universal occurrence. 



ECHINODERM CLEAVAGE. 81 

(b) Demonstrations of the accessory or "x" chromosome 
may also be shown. What relation has this chromosome to 
sex? What happens to this chromosome in the reduction 
division? In fertilization? Do you think we can properly 
speak of this as a sex determiner? 

III. FERTILIZATION 

(a) Examine demonstrations showing the entrance of the 
sperm and the conjugation of the male and female pronuclei 
to form the cleavage nucleus. 



CLEAVAGE AND GASTRULATION OF ECHINODERMS 
THE EGG OF ASTERIAS OR ARBACIA. 

The eggs and spermatozoa of many marine animals are laid 
directly into the water where they meet in fertilization. Such 
eggs are usually small, having but little yolk. They develop 
rapidly into feeding larvae, which swim for a time, and then 
take up the life of the parent upon the bottom. Because of 
the ease with which they can be provided with their normal 
environment, these eggs are particularly favorable for experi- 
mental studies and have become classic examples in the study 
of fertilization, artificial parthenogenesis, cleavage, and the 
like. 

(a) Examine stained material permanently mounted or in 
the clearing fluid, showing cleavage, blastula and gastrula 
stages in the egg of the starfish or sea-urchin. Note the egg 
membrane, sometimes showing the heads of many spermatozoa 
which failed to enter. The two-, four-, eight-cell and later 
cleavage stages on to the blastula or hollow sphere stage will 
be recognized. Find stages of the blastula showing the ingres- 
sion of mesenchyme cells at one pole. Is the wall of the 



82 Ontogeny of Amphibia. 

blastula of uniform thickness? Can you tell from the first 
the region that will invaginate to form the next stage, the 
gastrula, in which the primitive gut cavity or archenteron 
is formed. Its opening is the blastopore. The invagination 
is termed gastrulation. The germ-layers, ectoderm and 
endoderm have now been formed. The mesenchyme cells 
noted above and other cells which arise from the blind end 
of the archenteron constitute the mesoderm. 

Exercise 1. Make a series of outline figures illustrating the 
foregoing. 

(b) The type of cleavage here represented is designated as 
" total" or holoblastic and alecithal (without yolk). Compare 
later with condition in frog and chick. The blastopore be- 
comes the anus of the larva. The mouth is formed by an 
invagination, the stomodaeum, which unites with the blind 
end of the archenteron. Examine demonstrations. A larva 
which is strikingly bilateral results and from this, by a curious 
metamorphosis, the radially symmetrical adult is formed. 
The existence of such a larva constitutes the main evidence for 
the belief that the present radially symmetrical echinoderms 
have descended from bilaterally symmetrical ancestors. Com- 
pare with the inferences drawn from the existence of fish-like 
Rtages in frog and chick. 



ONTOGENY OF THE AMPHIBIA 

I. BREEDING HABITS, ETC. 

(a) If possible go out to collect frogs' eggs, examine the 
places where frogs and salamanders lay and make out what 
you can regarding their activities during the breeding season. 
Several of the species common about Columbia may deposit 
the eggs in February, or early in March, others at some time 
later in the spring, or even in early summer. 



Ontogeny of Amphibia. 83 

(b) Take home a mass of eggs you have yourself collected 
or have obtained from the laboratory. Place in a shallow dish 
or basin and keep in a light place, not exposed to direct sunlight 
for much of the day. Record the stage of the eggs when 
obtained and note their progress from day to day. Preserve 
your notes in the form of a written report to be handed in later. 
The influence of temperature upon the rate of development can 
be tested by placing part of the eggs out of doors on the cool 
north side of a building and comparing them each day with 
those having sun and the warmth of indoors. With proper 
care they may be kept until the tadpoles have completed their 
metamorphosis. At no time should the water in the dish be 
allowed to become too low from evaporation or to become foul 
from the growth of bacteria. Green water plants will be 
beneficial unless growing in too dense masses. When the 
tadpoles are fully formed, small bits of bread may be crumbed 
up and put in the dish. Too much of this will, however, foul 
the water and hence care must be used. 

(c) Examine the living frogs and salamanders on exhibition 
in the laboratory and find out the species to which the eggs you 
are studying belong. 

II. THE UNFERTILIZED EGG, OR OVUM 

(a) Examine in a watch glass of water a small mass of eggs 
from the ovary of a frog preserved in formalin. Look for 
small eggs among the larger ones of the present season. Some 
of these will show, when examined under the low power, the 
nucleus with its nucleolus and a small body of cytoplasm. 
Further study with proper material would show that the com- 
paratively large eggs are single cells in which a great deal of 
nutrient yolk has been accumulated in the cytoplasm. The 
egg in these stages before fertilization is termed the ovum. 

Exercise 1. Draw one of these small ova to show its parts 
as a cell. 

(b) Permanently mounted sections of the ovary of a young 
frog may also be used to demonstrate the cellular structure of 



84 Ontogeny of Amphibia. 

the ovum. These will, show ova of various sizes surrounded 
by the nuclei of smaller cells and the nucleus, nucleolus and 
cytoplasm. 

(c) Remove a living egg from the ovary of a female frog 
and crush under a cover slip. What can you make of the 
structure when examined with the compound microscope? 

III. THE SPERMATOZOON 

(a) Cut into a piece of testis and examine the milky contents 
in normal salt solution. Under the high power look for motile 
bodies, the spermatozoa. Each has a very long tail, not at 
first observed. Various nucleated cells may be found in the 
testes. Some of these can be recognized as stages in the for- 
mation of the sperms. During the breeding season, ripe 
sperm may be found in the seminal vesicles. As in the case of 
the ovum, the spermatozoon is a single cell. 

Exercise 2. Draw a ripe spermatozoon and any other cells 
which are clearly younger stages of the same. 

IV. THE EGG-LAYING, FERTILIZATION AND 

COPULATION 

(a) Recall the exact structure of the male and female 
reproductive organs. The jelly, which is so conspicuous a 
feature of the masses of eggs seen in ponds, is a product of the 
oviducts. Fertilization occurs in the water as the eggs leave 
the cloaca of the female and while the animals are joined in 
copulation, or before the swelling of the jelly during the first 
few hours exposure to the water. Take several eggs in which 
fertilization is in progress and which have the jelly well swollen. 
Note the individual envelopes in which the eggs are embedded. 
What is the characteristic difference between the jelly of the 
frog and that of the salamander eggs? Note the distribution 
of the color on the surface of the egg. How does it compare 
with the general distribution of light and dark color on adult 
frogs, fishes, birds, etc., with which you are familiar? Which 



Ontogeny of Amphibia. 85 

is the heavier side of the egg? The centre of the pigmented 
area is called the animal pole, the opposite point on the sphere 
the vegetative pole of the egg. If specimens showing the polar 
bodies are available, examine these and show in your next 
drawing. 

Exercise 3. Draw, (a) several eggs, on a scale of 2 or 3, 
showing their envelopes and the general mass of jelly, and (b) 
a single one from a side view 1 inch or more across to show 
distribution of pigment and the jelly envelopes. Label the 
poles. 

V. THE DEVELOPMENT OF THE FERTILIZED EGG 

(a) Where the stages noted in the ensuing account are 
followed in preserved material, it will, of course, be impossible 
to observe the actual progress of the development here de- 
scribed. Careful reading will, however, make clear what 
points may be observed in preserved material and the method 
of description will enable the student to follow more vividly 
the changes which the preserved stages represent. When it 
is desirable to remove the jelly from any of these stages in 
preserved material, it may be easily done by rolling the egg 
along on a piece of filter paper. 

Cleavage Stages 

(b) If the living eggs are available, begin with the zygote or 
one-cell stage and watch closely for the first cleavage furrow, 
a dark groove which appears first on the animal pole and, as 
it grows deeper, spreads over the vegetative portion until it 
encircles the sphere. Observe its exact position with refer- 
ence to the polar axis. Record the time occupied in the above 
process by which the two-cell stage is produced. 

Exercise 4. Draw side and top views to show the furrow 
in process of formation and as it appears when completed . 
The most satisfactory size will be a figure 13^ to 2 inches in 
diameter, a scale which should be continued in the subsequent 
drawings. 



86 Ontogeny of Amphibia. 

(c) A short period now ensues during which no external 
changes occur, but internally the nuclei are preparing for the 
next cell division. 

(d) Watch now for the second cleavage furrow. Record 
the time of its first appearance and of its completion. 

Exercise 5. Draw a top view of this furrow just appearing 
and a view from the vegetative pole when it is complete. 

(e) Careful watching is necessary lest the third cleavage 
furrow, which is horizontal and just above the equator of the 
sphere, come in unobserved. Record time of its appearance 
as in foregoing. With the completion of the third furrow we 
have the eight-cell stage which has four smaller, deeply pig- 
mented cells above and four larger, lighter colored cells below. 

Exercise 6. Draw a side, or top view of this stage number- 
ing the furrows. 

(f) Understand that with each division of any one cell the 
nucleus also divides, so that in the two, four, eight and later 
cell stages and so on to the many celled adult organism, each 
cell possesses a nucleus descended through a longer or shorter 
series of divisions from the original nucleus of the one celled 
stage or zygote which was itself formed by the fusion of nuclear 
material from egg and spermatozoon. Hence, we reach the 
generalization that every cell of the adult animal may contain 
a nucleus descended one-half from the male and one-half from 
the female parent. 

(g) The next cleavage consists of two vertical furrows which 
appear simultaneously at right angles to one another and cut 
each of the eight cells approximately in halves. The four 
upper cells often complete this division before the furrows have 
appeared in the lower hemisphere, thus making, with the eight 
smaller above and the four larger cells below, a twelve-cell 
stage. 

Exercise 7. If this is observed, draw from a top or side view, 
to show the twelve-cell stage. 

(h) With the division of the four lower cells, the sixteen-cell 
stage is produced. 



Ontogeny of amphibia. 87 

Exercise 8. Draw this from a side view. 

(i) By very careful observation, it can be determined that 
there next appears an approximately horizontal furrow parallel 
to the plane of the third cleavage. This divides the eight 
upper cells. A corresponding cleavage plane divides the 
eight lower cells, thus making a total of thirty-two. A thirty 
two-cell stage is, however, a theoretical rather than an actual 
occurrence, because of the fact previously noted that the cells 
about the upper pole divide faster than the corresponding yolk 
laden cells below. Again, very careful observation shows that 
there next follow two more approximately horizontal planes 
of division, one above and one below those last mentioned, 
making a forty eight-cell stage, but here as in the thirty two-, 
this exact number of cells is probably never present because 
of the way in which the lower cells lag behind the smaller 
upper ones. From the eight-cell stage on, the cleavage is 
not carried out with geometrical regularity as will readily 
appear in the study of (g) and (h) above. 

(j) The term mulberry stage is often applied to these stages. 
More definitely, we will speak of it as an early blastula stage, 
the complete blastula being reached only by the continued sub- 
division of the constituent cells. 

Exercise 9. Draw the early blastula stage from a side view. 

Blastula and Gastrula 

(a) A characteristic feature of the blastula is the existence 
of an internal cleavage or blastula cavity. In the amphibian, 
this cavity appears at about the twelve to sixteen-cell stage 
and persists until it is obliterated by the gastrulation process. 
Take a preserved specimen in the early blastula stage and after 
removing the jelly by rolling on filter paper, hold gently 
between forceps, without crushing, and divide in halves by a 
vertical cut with a sharp scalpel. Examine with hand lens and 
note the cleavage cavity and cell outlines. 

Exercise 10. Draw the cut surface to show such an early 
blastula in vertical section. 



88 Ontogeny of Amphibia. 

(b) If the eggs are followed hour by hour it will be seen 
that during the second day, at room temperature, the dark 
cells of the animal pole begin to encroach upon the surface 
area of the lower light colored ones. The exposed surface of 
the lower cells thus becomes diminished around its entire 
margin by downward over-growth of the dark upper cells. 
By turning the egg upside down there will be seen along part 
of the circumference of the diminishing area of exposed yolk- 
cells a crescentic depression which is the blastopore. Under- 
stand from your lectures the internal changes which are now 
taking place. The stage now reached is called the gastrula. 

It can be turned upside down for observation by placing on a 
slide a pin bent to an acute angle putting the specimen in the 
desired position in the angle and adding a little water and a 
cover glass. Find the blastopore with a hand lens and with 
low power of microscope. Look for cell outlines in the dark 
and in the light areas and indicate in the following figure. 

Exercise 11. Draw the gastrula stage as seen from beneath. 

(c) At a later stage of the gastrula when the dark cells 
have still farther encroached upon the exposed area of the yolk 
we have the yolk-plug stage. This may be examined in the 
same way as the last or cut in halves as in (a) above and exam- 
ined in section. 

Exercise 12. Draw this yolk-plug stage. Understand from 
your lectures and the text-book the internal structure of the 
gastrula, i. e., its ectoderm, endoderm, mesoderm and archen- 
teron. The yolk-plug finally disappears within the embryo, 
but the blastopore can still be distinguished as a minute pit 
which is to be shown in your next drawing. 

Neural Fold Stage* 

(a) The first sign of this stage appears about the time that 
the yolk-plug is lost to view. The ectoderm thickens along 

*The directions as far as this point have been designed either for 
the eggs of a frog or a salamander, In the sections which follow 
the notes have been written with special reference to the salamander 
Amblystoma tigrinum, but will serve almost equally well for the frog. 



Ontogeny of Amphibia. 89 

a certain area and as a result of this a ridge appears upon the 
upper portion of the still spherical embryo. This ridge may 
be regarded as a continuous structure having something the 
shape of an hour glass, but it is customary to speak of the right 
and left portions as the two neural folds. Find the blastopore 
which now lies at one end of the area enclosed by these folds. 
With the appearance of the neural folds, the bilateral symmetry 
which characterizes the outside of the adult becomes obvious 
externally. Although this stage is not greatly changed from 
the spherical condition immediately preceding it, we can now 
clearly recognize the axes of the adult body as follows: The 
region between the neural folds is on the dorsal mid-line. The 
opposite surface is of course the ventral. The end where the 
folds are most widely separated represents the anterior, the 
end where the blastopore is located the posterior region of the 
future adult. 

Exercise 13. Draw a neural fold stage from a top view as it 
normally lies within the jelly. Make outline of the jelly still 
surrounding. Label to show all the above points and the regions 
of the future adult. 

(b) The neural folds become higher and approach one 
another along the dorsal mid-line where they finally fuse. 
Examine a slightly later stage in which the embryo has become 
flattened and more elongated and rests on one side. Where 
do the folds come together last? Where is the blastopore? 

Exercise 14. Draw this stage from a side view with ventral 
surface below and label thoroughly as in last. 

(c) Understand from lectures and text-book what develops 
from that part of the ectoderm which is folded in when the 
neural folds meet and fuse, also the origin of the neurenteric 
canal which for some time connects the neural tube and the 
archenteron, also the structures which would appear in sagittal 
and transverse sections of such a stage. 

Beginning of the Tadpole Stage 

(a) After the foregoing stage the embryo becomes more 
elongated and assumes the shape of a crescent. Study such a 



90 Ontogeny of Amphibia. 

stage to identify the dorsal mid-line where the neural tube 
has disappeared beneath the surface and the anterior end 
where there is more suggestion of differentiation than at the 
posterior extremity. The larva can be propped up against a 
bent pin or some slightly flattened shot and the proctodaeum 
found as a minute pit in the posterior region of the ventral 
side. Along on each side and just below the dorsal mid-line 
are some transverse markings which show the lines of division 
between the mesoblastic somites, or first muscle segments. 
Identify head, neck and body regions. As not all the larvae 
given out will be in exactly the same stage, go over this last 
with one of the instructors to make sure you understand what 
can be recognized in the particular specimen you have. 

Exercise 15. Draw a side view showing all these points and 
having the orientation the same as in your last figure of the 
neural fold stage, i. e., ventral surface below and head pointing 
in same direction. 

(b) Get several specimens showing the transition from the 
above to the next stage. Note how the crescent straightens 
out and the elongated larva gradually shows more definite 
rudiments of the adult organs. In the stage to be drawn, 
examine from the side, then prop up against a bent pin and 
study the ventral surface. The eyes are swellings right and 
left on the head, just below them are two smaller dark areas, 
the nasal pits, or future nostrils. A depression on the ventral 
side and posterior to the nasal pits is the stomodaeum. Rudi- 
ments of the suckers and three external gills appear laterally 
in the neck region, behind them is a protuberance, the begin- 
ning of the fore-limb. Note the tail and the proctodaeum and 
the general changes in shape. Go over with an instructor to 
make sure of each point before drawing. 

Exercise 16. Draw from a side view, labeling thoroughly 
and oriented as other side views. 

(c) Study next a larva about ready to hatch. Identify 
all the features noted in the last and see to what extent they 
have changed. If the living specimen is too active, add a few 
drops of ether or kill with five per cent formalin. In a specimen 



Ontogeny of Amphibia. 91 

■still alive you will be able to see the heart beating within the 
pericardium, which lies in the ventral region of the neck. 
The stomodaeum becomes about this time connected with the 
front of the archenteron and so forms the mouth. The same 
thing happens to the proctodaeum which then becomes the 
anus. Note the very dark pigment cells scattered everywhere 
and look for the beginning of a collar like ridge on the ventral 
surface and extending up laterally along where the external 
gills are attached. This is the operculum and if not yet recog- 
nizable will be seen in the next stage. 

Exercise 17. Draw from side view with orientation same as 
previous figure and label all the structures which can be shown 
in this view. 

Tadpole Stages 

(a) Examine larvae, or tadpoles, which have been some- 
time hatched. Watch them alive, notice their active move- 
ments and how the suckers are used. In a specimen anaesthe- 
tized with a few drops of ether, examine the gills with low 
power of your microscope. Watch the flow of blood in the 
capillaries. Note corpuscles and the pulse. 

Exercise 18. Draw the outline of a single gill and its vessels 
and show course of blood flow with arrows. 

(b) With the microscope or hand lens note the heart beat- 
ing in the pericardium. In some specimens, portions of the 
digestive tract will be seen showing through the ventral part 
of the body wall. Note again the operculum and recall later 
when examining the similar structure in the tadpole of a large 
bull frog. Note the size and outline of the mouth when seen 
from below. 

Exercise 19. Draw this larva from a ventral view. 

(c) Examine Museum or living specimens of the genera 
Amblystoma, Diemyctylus and Necturus. Notice the external 
gills which persist throughout life in the last. Examine also 
specimens dissected to show the viscera in place. These forms 
are Amphibia of the class Urodela and are characterized by the 



92 Ontogeny of Amphibia. 

persistence of the tail in the adult. How do they differ from 
the class Anura? 

VI. THE TADPOLE OF A LARGE FROG 

(a) The tadpoles or "pollywogs" of the frogs and toads 
(Anura or tailless Amphibia) have slightly different outlines 
from the Urodele tadpole just studied. In the case of our 
smaller frogs and of the toads, the tadpole undergoes the 
metamorphosis into the miniature adult the same season that 
the egg is laid, but in the case of the large "bull-frog" the eggs 
are not laid until late in the spring and the embryo remains 
in the tadpole condition over the next winter, finally under- 
going metamorphosis when about one year old, or in some 
cases remaining a tadpole through a second year. Such speci- 
mens approaching metamorphosis are abundant in the early 
spring and in fact may be obtained at any time during the 
open months. 

(b) Watch the living specimens in an aquarium or large pan 
of water; notice how they come up to breathe and how the 
most advanced specimens are beginning to use their legs. 

(c) Study a preserved or a freshly killed specimen in a 
dissecting pan and covered with water. Make out nostrils, 
mouth with horny teeth, hind limbs, anal opening and on one 
side of the neck region an opening which leads into the gill 
chamber, probe gently into this with a guarded bristle and 
find the extent of the cavity into which it opens. 

Exercise 20. Draw from a side view orienting same as 
drawings of the Urodele tadpole. 

(d) Pin the specimen out under water ventral side up. 
Remove the outer covering from the cavity just explored with 
the bristle. Find the internal gills and between them the gill- 
slits. Discover relation of these slits to mouth cavity. 

(e) Take a small fish and pin it out beside the tadpole. 
Note the flap or operculum which covers the gills on either 
side. Cut off these opercula and find out the relation which 
the gills and gill-slits of the fish have to its mouth cavity. 



Ontogeny of Amphibia. 93 

Compare this with what you see in the tadpole. Understand 
how the membrane covering the tadpole's gills is homologous 
to the fish's operculum. See models showing development of 
operculum. Understand difference between external and in- 
ternal gills. 

(f) Find the heart on mid-line between gills in both tadpole 
and fish. What parts can you recognize in each? 

(g) Remove the ventral body wall of the tadpole from the 
region between heart and anus with care not to injure the 
viscera. Identify, by pressing aside without cutting or tear- 
ing, the stomach, the tri-lobed liver, the gall bladder, pan- 
creas, fat-bodies, the much coiled intestine and the posterior 
end of kidneys. Compare with same in adult frog, as previ- 
ously studied. 

(h) Cut open the abdominal cavity of the fish and examine 
its viscera briefly for comparison. 

Exercise 21. Draw the organs of the tadpole as they appear 
from ventral view and lying in place. Scale of 3. Make out- 
line of body around them. 

(i) In the tadpole find the lungs and the oesophagus where 
it enters the abdominal cavity. Cut this last off and without 
injuring the lungs, kidneys, and fat-bodies, remove the diges- 
tive tract severing it again at the rectum. Unravel the intes- 
tine, spread out and measure using the distance from mouth 
to anus as a unit. Record and compare with your record of 
same in the adult frog. Examine now the organs which remain 
in the body cavity, 'lungs, kidneys, spleen, rudiments of 
ovaries or testes and the fat-bodies. 

Exercise 22. Draw on same scale as last to show these 
organs in place. 

(j) With a sharp scalpel, cut through the body transversely, 
just back of eyes and again a little farther back. Study such 
a section under water, noting position and development of 
portions of central nervous system thus exposed and whether 
any of the bony skeleton is present. 

Exercise 23. Draw such a section. 



94 Embryology of Chick. 

VII. TADPOLES IN METAMORPHOSIS 

(a) The miniature bull-frogs in which the tail is still present: 
and which are just completing the metamorphosis, are not as 
readily obtainable in large numbers as the similar stage in the 
smaller frogs which metamorphose during their first summer. 
Examine museum or living specimens of the larger form and 
then study in a watch glass covered with water a similar stage 
of one of the smaller species. Note whether the shape of head 
and mouth have changed and if the tympanum has yet appeared ; 
also the development of the limbs and tail, which last, from this 
stage on, rapidly dwindles away. 

Exercise 24. Draw on a scale of 2 or 3 from a dorsal view.. 



EMBRYOLOGY OF THE CHICK 

(a) Examine the reproductive organs of a male and those 
of a laying female to see the testes and their vasa deferentia, 
the oviduct with its funnel, its albumen and shell-secreting 
parts and its relation to the cloaca and rectum. Notice in the 
ovary the eggs in various stages and the places where eggs have 
been recently discharged, also the stigmata or non- vascular 
areas which rupture when an egg is set free. 

(b) Examine under the microscope a small amount of the 
yolk obtained from one of these ovarian eggs. Recall the 
similar structures in the frog's egg. 

(c) Examine demonstration sections showing the cellular 
nature of the ovary. 

(d) Take an unincubated hen's egg and, using scissors, cut 
open on one side a space about one inch across, being careful 
that the scissors points do not cut too deep and injure the yolk. 
The opening may be further enlarged, if necessary, the egg rest- 
ing upon a bed of cotton wool in a finger bowl. Find the chal- 
azae or twisted cords of albumen at either end. What relation 
have they to the yolk and to the shell? Find the two mem- 



Embryology of Chick. 95 

branes which line the shell. These can always be seen at the 
large end where there is a space between them. At one place 
upon the surface of the yolk is a small whitish area, the blasto- 
derm, the central part of which is known as the area pellucida 
and the peripheral part as the area opaqua. Does this always 
appear at the top, however the egg is turned? Compare with 
the rotation of the frog's egg in its capsule. Understand the 
comparison between such an egg as this and that of the frog 
and the starfish and the condition of the blastoderm at this 
stage. 

Exercise 1. Draw the egg thus dissected, on a scale of 1. 

(e) Open an egg which has been under incubation for 
twenty-four hours and placing it on the cotton beside the one 
just drawn compare the two. Record or make a simple sketch 
to show the changes which have taken place in the blastoderm 
during this first day of incubation. Before discarding this 
specimen, the existence of a delicate yolk membrane should be 
demonstrated by puncturing. 

(f) Permanently mounted specimens of the blastoderm and 
the developing embryo will be issued for the study of approxi- 
mately the 24, 32, and 45 hour stages, in their finer details. 
These should be handled with great care lest they be crushed 
by wiping or by the microscope objectives. These slides are 
secured by removing the blastoderms, which are then fixed, 
stained and mounted in balsam. The first to be studied is the 
24 hour stage, in which the following parts are to be made out 
with the low power of the compound microscope; neural folds, 
head folds, mesoblastic somites, primitive streak, area pel- 
lucida, the vascular area and the vitelline area. Focus care- 
fully to determine the vertical dimension of the parts and com- 
pare your results with what is shown by models. 

Exercise 2. Draw this stage as a full page figure, including 
a small margin from the vitelline area. 

(g) Open a 36 hour egg, just from the incubator and notice 
the further changes. With the aid of an instructor, inject 
some India ink into the cavity beneath the blastoderm and 
harden the embryo by dropping strong alcohol upon the out- 



96 Embryology of Chick. 

side. Compare part by part with a permanently mounted 
specimen of the same stage, placing the latter across the top 
of a watch glass and against a white background. Study with 
lens to locate the parts observed in the twenty-four hour stage. 
After identifying these with the hand lens in both the fresh 
and the preserved specimens, study the mounted specimen 
further under the compound microscope and make out, in 
addition to the features seen in the last, the beginning of the 
brain vesicles, the amnion, heart, notochord and any changes 
in the size and proportions of parts. Here again careful 
focusing and the comparison of what you see with the models 
is necessary for the proper understanding of the third dimen- 
sion. 

Exercise 3. Draw this stage in a figure similar to the last. 

(h) Examine next a freshly opened embryo of 45 to 48 hours 
incubation, comparing it with the last. Note the blood ves- 
sels, the pulsations of the heart (which should be counted for the 
number per minute) and the extent to which the vitelline area 
has extended over the egg and then treat with India ink and 
alcohol as before. Study together the specimen thus freshly 
prepared and a stained and a mounted specimen of the same 
stage. Find all the structures observed in the thirty-two hour 
stage and in addition note the cranial flexure and the torsion 
of the cephalic end of the embryo, the fore, mid, and hind- 
brain vesicles, the optic vesicles and the lens of the eye, the 
auditory vesicles, the tubular heart, now bent into an "S" 
shape, the vitelline arteries and veins and the sinus termi- 
nalis, the gill bars and slits and the extent to which the 
amnion has developed. 

Exercise 4. Draw this stage, in a figure similar to the last. 

(i) Understand from demonstrations of the later stages 
of chick and mammal and from the lectures, charts and text- 
books, how the embryo is related in its several stages to the 
yolk mass and the significance of the amnion, allantois and 
yolk-sac in both mammals and birds. 



Insects. 97 

THE INSECTS 

Phylum, Arthropoda. Class, Insecta or Hexapoda 

I. AN ORTHOPTEROUS INSECT 

(a) The grasshoppers and locusts are the most common 
representatives of this order Orthoptera, and any large speci- 
men of several species, which are common locally, may be 
used. Living individuals should be observed in glass jars, con- 
taining grass and covered with a screen. Exactly how are the 
legs used in walking and jumping? The spiracles, or respira- 
tory openings will be seen along the sides of the abdomen. 
Observe and time the intervals between the respiratory move- 
ments. Note the nature and the distribution of color upon the 
animal. Can you suggest any value which this may have for 
the animal in nature? Offer bits of green vegetation to the 
specimens in the jars and see what you can make out regarding 
their mode of feeding. Touch the "feelers," antennae, of the 
head with a long piece of glass tubing having a plug of absorbent 
cotton in the end and observe how sensitive to touch are these 
organs as compared with other parts of the body. Moisten 
the absorbent cotton with some strong smelling fluid and bring 
it near the antennae without touching them. Can the animal 
smell with these organs or with any other part of the body? 
Remove a specimen from the jar and holding gently examine 
the parts at closer range. Look at the compound eyes, the 
antennae, etc., with the lens. Note the "molasses" which is 
regurgitated from the mouth. This is a digestive fluid mingled 
with food. If a good sized drop can be collected from one or 
more specimens and placed upon a slide, put a bit of fresh green 
vegetation in this and note result before the fluid evaporates. 
What may be the significance of this habit of regurgitating the 
contents of the digestive tract? If you have time, devise 
experiments to determine whether temperature, or sensations 



98 Insects. 

akin to fear in the higher animals influence the rate of the 
respiratory movements. 

Exercise 1. Write out in the form of carefully worded notes 
such facts of the above study as can be thus recorded. 

(b) A preserved or a freshly killed specimen may now be 
used for a study of the structure. Compare the segmentation 
with what you know of the crayfish and earthworm. The main 
divisions of the body are head, thorax and abdomen. The 
thorax has three segments, prothorax, mesothorax and meta- 
thorax and has the three pairs of legs. How many segments in 
the abdomen? Are there signs of segmentation in the head? 
The antennae and compound eyes have already been located, 
examine again with the lens. Find the simple eyes, or ocelli, 
three small dots between the antennae. About the mouth are 
the following parts: the upper lip or labrum, next a pair of 
mandibles and, by pressing these last aside, the pair of maxillae 
and the labium, which last functions as a lower lip and is really 
a second pair of maxillae united. Note the labial and maxil- 
lary palps, or "feelers." The forward, upper and lateral parts 
of the head are covered by a simple plate of the skeleton, the 
epicranium, with which the mouth parts just mentioned are 
articulated. Like the exoskeleton of the crayfish, the covering 
of the grasshopper's body is a continuous membrane which 
thins out at the joints and is of different thickness in different 
parts of the body. For convenience we speak of the plates 
or sclerites, of the skeleton though neighboring plates are 
continuous by the thinner skeleton over the joints. 

(c) Examine the thoracic region and determine accurately 
the number and position of the plates in each segment, the place 
of attachment of the wings proper and of the wing-covers. 
Each of the thoracic legs consists of five main divisions: the 
coxa by which the leg articulates with the body, a short seg- 
ment the trochanter, a long segment the femur, then the tibia 
and last the three jointed tarsus terminating in a pair of hooks 
and a little pad. Notice how the trochanter of the metatho- 
racic leg has fused with the femur and how this limb is a special 
adaptation of the same plan which the others present. The 



Insects. 99 

abdominal segments are divided into upper and lower parts 
by a horizontal band along which are the spiracles. How 
many of these are there and on which segments do they occur? 
On the first abdominal segment near the spiracles there are 
oval areas covered by a thin membrane. These are the 
auditory organs. The tip of the abdomen differs in the two 
sexes. Each sex has the following parts in common: a single 
terminal dorsal plate; right and left below this the paired 
podical plates, between which lies the anus and on the outer 
face of which are two small projections, the cerci. Below the 
podical plates of the male there is a single large sub-genital 
plate which is replaced in a female by the conspicuous plates 
of the ovipositors. Understand how the latter are opened for 
the extrusion of the egg after digging the cavity in which it is 
laid. 

Exercise 2. Draw a full page figure showing the grasshopper 
as seen from the right side. Spread out dorsally the wing 
and wing-cover of this side and arrange the legs so that the 
body will show to advantage. 

(d) Holding the specimen in one hand cut open the body 
along the mid-line a little to one side of the mid-dorsal region. 
Use fine scissors and be very careful not to cut deep and injure 
the soft parts underlying the skeleton. After opening for the 
entire length of the body, pin out under water in a dissecting 
pan by slanting two pins across the union of the head and pro- 
thorax. Fasten the free end of the abdomen with a single 
pin passed through the end of the cut and then spread out and 
pin apart the edges of the cut, using great care not to injure 
the internal organs. If the heart has not been destroyed in 
opening the specimen, it will be found either adhering to the 
inner face of the skeleton, along the dorsal mid-line of the 
abdornen, or in this position upon the surface of the internal 
organs. A lace-like mass of yellow tissue is the fat-body which 
should be removed carefully to expose the alimentary canal a 
large tube running straight through the body. In exposing 
this more fully, the muscles of the thoracic region must be 
removed. On top of the tract in the abdominal region are the 



100 Insects. 

reproductive organs which have right and left parts coming 
up from either side and meeting dorsally. Their ducts pass 
backward from the ventral side and unite in a single duct which 
opens ventral to the anus, on the upper face of the sub-genital 
plate in males, between the halves of the ovipositors in females. 
Among the organs are certain structures which are conspicuous 
in the fresh specimen by their silvery color. These are the 
tracheal or air-tubes and the air-sacs through which the air 
taken in by the spiracles is carried to all parts of the body. 
Remove the parts of the fat-body that may conceal the diges- 
tive tract. Beginning anteriorly, this is composed of a crop, 
which is thin walled; a stomach, encircled by eight elongated 
pouches, the gastric caeca; a region called the intestine and a 
terminal portion, the rectum. Where the stomach passes into 
the intestine there will be found a mass of threads which have 
an excretory function and are known as the Malpighian tubules. 
Exercise 3. Draw the digestive tract on a scale of 3 or 4, 
as it lies in place and seen from the dorsal side, making around 
this a simple outline of the body as cut open. 

(e) Remove the digestive tract by severing the rectum 
near its posterior end and pulling gently forward. The short 
oesophagus, by which the crop connects with the mouth, will 
now be seen. Before this is severed find the brain just back of 
the eyes and dorsal to the tract, and the circum-oesophageal 
connectives which pass on either side of the oesophagus and 
connect the brain with the sub-oesophageal ganglion (to be 
seen later). Cut the oesophagus, without injuring any of 
these parts, and examine the gut under water, to get a better 
view of its parts; particularly the gastric caeca and Malpighian 
tubules. Look on the sides of the crop near its posterior end 
for the gastric ganglia, white spots from which fine nerves 
radiate. Look on either side of the body in the region from 
which the crop has been removed for the salivary glands. 
These communicate by fine ducts with the region just inside 
the mouth, a point which is difficult to ascertain without a 
special dissection. 

(f) Look at the air sacs as now exposed and make out any 
regularity in their arrangement. Remove a small bit of the 



Insects. 101 

muscle or fat-body and examine on slide under a cover with 
microscope. Find the tracheae lined with their spiral threads. 
Draw if you have time. Continue to remove the fat-body and 
muscles of the ventral side, in the region of the thorax, until 
the nerve cord is exposed. If the reproductive organs have not 
been destroyed the union of their right and left parts may be 
observed below the gut before their removal. How many 
ganglia are there and how many nerves does each give off? 
How does the position of the entire nervous system in the body 
compare with the same in a frog, a crayfish and an earthworm? 
From the brain there are nerves to the compound eyes, the 
ocelli and the antennae. The circum-oesophageal connectives 
have already been located. 

Exercise 4. Draw as much of the nervous system as you 
have made out upon the same scale as the drawing of digestive 
tract. 

II. A COLEOPTEROUS INSECT 

(a) Any large beetle will do for this study, provided it is 
not too highly modified. By examining the animal from the 
ventral side locate the head, thorax and abdomen and the num- 
ber of segments visible in each. Look for antennae, compound 
eyes, ocelli, mandibles and other mouth parts, the anus and 
the thoracic legs, and compare with what you have found in 
the grasshopper. Where are the wing covers and the wings? 
When the latter are found see how they fold up beneath their 
covers. Fasten down, dorsal side up, by pinning through 
the prothoracic segment, spread one wing cover out at right 
angles and unfold the corresponding wing which can be spread 
in the angle between the wing cover and abdomen. Raise the 
head, if it bends too far ventrally, and spread out the thoracic 
legs on the side where wing and cover are closed. 

Exercise 1. Draw the specimen from this view and on such 
a scale as to make the figure three or four inches long. Show 
the plates of the skeleton with care and number the segments 
of thorax and abdomen. 



102 Insects. 

(b) In the larva of a beetle find the main divisions of the 
body, head, thorax and abdomen, mouth with its jaws and the 
anus. Count the number of segments comparing with adult 
of the same species. 

Exercise 2. Draw such a larva from a lateral view showing 
these parts on a scale of 3 or 4. 

(c) Examine, as directed by instructor, such living speci- 
mens of beetles and their larvae as are available for individual 
study or demonstration. 

III. A HYMENOPTEROUS INSECT 

(a) Wasps of the genus Polistes are very common and are 
easily collected when they enter unscreened buildings with the 
approach of cooler weather in the fall. Head, thorax and 
abdomen will again be recognized as in the case of the other 
insects. How many segments in each? Look for antennae, 
compound eyes, ocelli, mouth parts and anus. At the pos- 
terior end of the female is the sting. The spiracles are a row 
of minute dots on each side of the abdomen. Compare the 
divisions of the thorax and of each thoracic leg with the cor- 
responding parts of the grasshopper. To which segments are 
the wings attached? 

Exercise 1. Draw a side view with wings spread dorsally, 
on a scale of 3 or 4. 

(b) Examine the "paper" nests of this wasp and others if 
available. Also artificial ants' nests and the eggs and larvae 
recently taken from an ant colony. The most remarkable 
facts regarding the hymenoptera are those connected with 
their social life in such colonies, a matter which will be dis- 
cussed in lectures or text-book. 

IV. A LEPIDOPTEROUS INSECT 

(a) Examine a good sized butterfly, or moth, going over 
the features noted for other forms (the three main divisions of 
the body, eyes, antennae, mouth parts, legs and wings). 



Insects. 103 

Mount some of the dust from the wing surface and examine 
under a microscope. What is the significance of the term 
"lepidoptera"? 

Exercise 1. Draw a dorsal view with wings spread, making 
the figure three or four inches across. Omit color pattern. 

(b) If available the eggs of butterflies or moths will be 
shown as a demonstration. Understand to what species such 
eggs belong and where they are laid. 

(c) Examine now a larva which is large and favorable for 
study. Where are the head, thorax and abdomen? Do you 
find thoracic legs? There are other pairs of appendages some- 
what like them and known as prolegs. How many are there 
and what is their structure as compared with the thoracic 
legs? Are there eyes, ocelli, antennae and mouth parts as in 
other forms? Do you find spiracles? 

Exercise 2. Draw a side view on a large scale. 

(d) If it is the proper season the larvae of various forms will 
be placed in the laboratory for individual study or demonstra- 
tion. Observe the way of moving and their voracious habits 
in feeding. How does the structure and use of the mouth 
parts differ in larva and adult? At the proper season, cater- 
pillars will often spin their cocoons in the cages where they are 
kept, or such cocoons may be collected and given out for study. 
Cut one open and find the resting stage, "pupa," within. 
Notice the silk of which the cocoon is composed. Such cocoons 
if uninjured may be kept in cages and the emergence of the 
adult insect observed at some subsequent time. 

(e) Understand the complete life history in each of the 
groups thus far studied and be able to explain the difference 
between direct development as in the grasshopper and the 
metamorphosis of butterflies, beetles, etc. 

V. OTHER ORDERS 

(a) Of the remaining orders of the Insecta, three are more 
commonly known and recognized by popular names. These 
are the Hemiptera, or true bugs; the Diptera or two-winged 



104 A Planarian. 

flies, of which the house fly is our most common representative; 
and the Odonata or dragon flies. Representatives of these and 
of their larvae will be placed in the laboratory for demonstra- 
tion and supplied to individuals if called for. 

(b) The life history and habits of insects presents much 
which is even more profitable for study than the points hereto- 
fore covered, but such work is difficult to handle properly with 
large classes and at fixed periods. Suggestions and assign- 
ments will, however, be made upon request to the instructor 
in charge and facilities for carrying on such work either at home 
or in the laboratory will be provided. 



PARASITISM AND OTHER FORMS OF ASSOCIATION 

AMONG ANIMALS 

I. A PLANARIAN WORM 

Phylum, Platoda. Class, Turbellaria 

Planarian worms are common in fresh-water where they are 
most easily discovered on the under sides of leaves, stones and 
small objects upon the bottom. For this study, the species 
Planaria maculata or any other representative form of these 
turbellaria may be used. 

(a) Examine in a watch-glass of water. How does the 
animal move? What changes in shape may the body undergo 
in "righting"? In meeting obstacles? In response to other 
stimuli? What is the shape and distinctive feature of the 
two ends? Are there sense organs? Can you find the mouth 
and, in sexually mature animals, the genital aperture on the 
ventral side? Transparent specimens will show the dendritic 
branches of the digestive system, the plan of which should be 
understood from chart or text-book figures. Place a small 
specimen upon a slide under a cover-slip and look for cilia. 



A Flukeworm. 105 

Can you see the justification for applying the name turbel- 
laria to these forms? Study also the coloration under micro- 
scope and hand lens. 

Exercise 1. Draw the animal from a dorsal view, scale of 
8 to 10, showing the above features. 

(b) Specimens will sometimes feed if crushed snails or bits 
of meat are placed in the dish. The muscular pharynx may 
then be seen. In this connection, their actions may be watched 
for evidence of a sense of smell. Interesting observations may 
also be made upon regeneration and upon their behavior with 
respect to light. Carry out such observations and experiments 
if you have time. 

(c) These worms are studied here with a view to empha- 
sizing their free-living condition. In nature, they move about 
actively, often capturing living prey, and reproduce either 
vegetatively by fission or by means of germ-cells. They are 
hermaphroditic. The eggs are laid in small stalked capsules 
attached to the under sides of the stones and other objects 
upon which the animals are living. From each of these cap- 
sules or egg-shells a number of young emerge as miniature 
adults able at once to take up the life of the parent upon the 
bottom. The life-cycle is thus in marked contrast with that 
of the parasitic representatives of this phylum. 

II. A FLUKE-WORM 

Phylum, Platoda. Class, Trematoda 

To the trematoda belong the external and internal parasites 
known as the fluke-worms. For this study, any one of the 
genera somewhat resembling Distomum may be used. Haema- 
toloechus variegatus, from the lungs of the frog, and another 
genus often found free in the body cavity of the frog are excel- 
lent material. 

(a) Examine living or preserved specimens and locate the 
mouth and suckers. How does the shape and behavior, if 
specimens are observed alive, compare with the same in the 



106 A Tapeworm. 

planarian? Locate the digestive tract and compare with the 
planarian. The reproductive organs are complex and varied 
in appearance and, if studied, special directions will be given. 
The animals are hermaphroditic and produce fertilized eggs 
which accumulate before being laid in a terminal portion of 
the female organs, the uterus, developing later when they are 
laid. The life-cycle is greatly complicated by the parasitism 
as described in lectures or text-book. Both in the structure 
and conditions of the life-cycle, contrasts should be drawn 
between the trematode and the planarian. 

III. A TAPE-WORM 

Phylum, Platoda. Class, Cestoda 

The cestoda or tape-worms are parasitic forms, even more 
highly modified in correlation with their parasitic habits than 
are the fluke-worms. The adults occur as parasites within 
the digestive tract of another animal, the larval stages mostly 
within the tissues of a secondary host upon which the pri- 
mary host is likely to feed. Species of the genus Taenia occur 
in many common mammals and are excellent for the study of 
the external features. They may be examined alive in water 
or after preservation in alcohol or formalin. 

(a) Examine an adult cestode in a pan of water. The 
smaller end has a head, scolex, the posterior end ripe joints 
or proglottids. What structures adapted for holding fast are 
found upon the scolex? Count the proglottids, compare with 
numbers in neighboring specimens and record. Can you see 
indications of the developing reproductive organs and of the 
genital apertures with copulatory organs, at one side? How 
and where do the proglottids seem to originate? Each pro- 
glottid contains a complete hermaphroditic reproductive sys- 
tem and the chain of proglottids may be regarded as a redupli- 
cation many times over of the reproductive machinery. If 
living worms are available, test the firmness of their attach- 
ment by the scolex to the mucus membrane of the host. Com- 



A Tapeworm. 107 

pare the external features with those of other tape worms shown 
as museum specimens. Moniezia expansa from the sheep and 
Crossobothrium laciniatum from the sand-shark are good for 
this purpose. 

Exercise 1. Draw a good sized figure of the adult, indicat- 
ing the parts as above and with the proglottids accurately 
shown. To avoid repetition, the figure may show several 
representative regions of the worm connected by dotted out- 
lines. 

(b) The "ripe" proglottids at the posterior end often show 
the outlines of the distended uterus, a cavity in which the 
development is begun. Here, the egg develops as far as the 
six-hooked embryo, a stage which may be obtained from either 
living proglottids or formalin material. Cut the proglottid 
into bits in a watch-glass and examine some of the material 
under high power of the microscope. Embryos surrounded by 
a tough shell and other membranes will be found. Can you 
find the six hooks? Is there any remnant of the yolk material? 
If alive, crush by pressing on the cover and watch movements. 
Do they seem effective as "boring movements?" Can you make 
any estimate of the number of six-hooked embryos produced 
by a single cestode? 

Exercise 2. Draw the embryo and its surrounding parts. 

(c) The ripe proglottids, with their six-hooked embryos, 
break off and pass out with the feces of the host. The six- 
hooked embryos are discharged by the rupture or disinte- 
gration of the proglottid and find their way to the secondary 
host by the chances of nature, entering with the food or drink. 
After its membranes are digested in the stomach of this host, 
the six-hooked embryo bores out into the tissue and develops 
to a stage known as the bladder-worm. Examine living or 
preserved material and make out the scolex and neck and their 
peculiar position. Can you see anything adaptive in this 
development within the bladder? Understand what hap- 
pens when the bladder-worm is eaten by the primary host. 

Exercise 3. Draw the bladder- worm, making a good sized 
figure. 



108 Forms of Association. 

(d) If the internal structure of the proglottid is to be 
studied, excellent results may be obtained from the motile 
proglottids of Crossobothrium laciniatum stained with alum 
cochineal. Further explanations will be given in the labora- 
tory. 

(e) Other important features in the internal structure of the 
cestode, which may be noted in chart or text-book figures or a 
further laboratory study, are, the brain and nerve cords, 
excretory system, absence of a gut, the granules of CaCC>3, 
and the cuticular membrane which covers the body. Are 
any of these features to be correlated with the parasitism? 
How may cestodes and trematodes be homologized? 

(f) All tapeworms, so far as known, have two hosts. In the 
following cases of known life-cycles which would be the pri- 
mary and which the secondary host? Man, — pig; dog, — 
rabbit; mouse, — cat; house-fly, — hen; fish, — bird; louse, — 
dog; man, — fish. Consider where and how each of the three 
stages would occur in each case. 

IV. OTHER FORMS OF ASSOCIATION 
AMONG ANIMALS 

The platoda offer an excellent example of closely related 
animals existing as free living and as parasitic organisms. 
From what you know regarding these and any other parasitic 
forms, write out a statement of the kind of modifications in 
structure and life history likely to occur in animals which have 
assumed parasitic habits. Consider cases of communal para- 
sitism in insects as explained elsewhere and the striking cases 
of association occurring among marine animals such as crabs, 
worms and mollusca, and the whole in relation to lecture, text- 
book and field-work bearing upon the inter-relations among 
different species and the struggle for life. 



Classification. 109 

THE CLASSIFICATION OF ANIMALS 

I. THE PHYLA OF THE ANIMAL KINGDOM 

A sufficient number of forms have now been studied in detail 
to enable you to form some picture of the types of structure 
which existing animals present. These may be reviewed and 
your knowledge extended in certain places with a view to giving 
you concrete ideas of other types not yet examined. The 
term Phylum is applied to certain larger groupings of ani- 
mals though, as we shall see at the conclusion of this survey, 
the phyla may again be grouped into larger subdivisions. An 
examination of the several phyla by means of museum or other 
specimens may be accomplished as outlined below. 

Phylum, Protozoa. 

The forms studied, Amoeba, Paramoecium, Englena, and 

Gregarina, together with figures and demonstrations of other 
forms, sufficiently illustrate this phylum. Emphasis is cen- 
tered upon the unicellar state, though simple colonies fre- 
quently occur. 

Phylum, Porifera. 

This phylum comprises the sponges. Examine simple 
sponges like grantia and leucosolenia, and notice the osculum, 
an excurrent opening, and, in grantia, the many small pores 
by which the water passes in. The larger sponges like the 
bath-sponge, and others which may be upon exhibition, are 
regarded as derivatives of the simpler types modified along 
the line of extensive budding and vegetative growth. Char- 
acteristics of the sponges are: Absence of a stomach or gut 
cavity comparable to that of other many-celled forms; attach- 
ment except during the earliest stages of development ; absence 
of what may be properly termed organs, although there are 
different kinds of cells; a skeleton of fibres as in the bath sponges 



110 Classification. 

or spicules as in grantia or the "glass sponges." The sponges 
are clearly the simplest of the many celled animals now living. 

Phylum, Coelenterata. 

Hydra and the hydroids with their jelly fish are the examples 
studied. Examine other and larger jelly fish, a sea anemone, 
corals showing the soft parts and the skeletons, sea-pens, fans, 
etc., and chart figures of ctenophores. Distinctive features 
are: absence of an anal opening; radial symmetry; two layered 
or diploblastic structure, i. e., ectoderm and endoderm as in 
hydra; tentacles surrounding mouth and in most cases 
attachment during a part of the life-cycle. 

Phylum, Platoda. 

Planarians and similar forms, fluke-worms and tape-worms 
as studied. Characterized in the forms not degenerate through 
parasitism by: bilateral symmetry; absence of an anal open- 
ing; absence of a coelomic cavity, though there is a middle germ 
layer (mesoderm) and the animal is therefore triploblastic. 

Phylum, Annulata. 

The earthworm is a representative form, though the group 
as a whole is characterized by appendages on the segments 
and organs of special sense in the head region which the earth- 
worm has presumably lost in the course of its evolution. 

Nereis is in this respect a better example. Small species^ 
related to the earthworms, are common in fresh-water and may 
have been observed. There are many tube-building forms 
among the marine worms, museum or chart figures of which 
may be examined. The leeches of fresh-water are greatly 
modified annulates. The annulata are characterized by: 
bilateral symmetry; an obvious metamerism; three germ- 
layers; a well developed coelome; nephridia; dorsal brain and 
ventral nerve cord as in earthworm. 

Phylum, Mollusca. 

Represented by the clams, mussels, snails, slugs, etc. 
Examine specimens of bivalve shells, comparing with the fresh- 



Classification. Ill 

water mussel, also the shells of marine snails showing lines of 
growth and peculiar shapes. Watch living pond snails, if 
not already studied, and notice the symmetrical head and 
creeping foot. Examine museum specimens of the limpets, 
marine forms belonging with the snails and adapted for cling- 
ing tightly to the rocks with the foot. Also another type of 
mollusc the chiton, with its segmented shell. Examine another 
type represented by the squids, devil-fishes and cuttle fish, 
active, free, swimming forms with an internal shell. As a 
phylum, the mollusca are characterized by: bilateral symmetry; 
a ventral foot; a dorsal one-pieced shell; a mantle, enclosing a 
mantle cavity in which lie gills; absence of metamerism; 
presence of a coelome with nephridia; three germ-layers. 
Most of these characters may be recognized in the specimens 
placed upon exhibition. 

Phylum, Echinodermata. 

Examine specimens of starfish and sea-urchins, noting the 
five-rayed symmetry. Can you find mouth and anus? Organs 
known as the tube-feet are used for locomotion. See mace- 
rated specimens showing plates of skeleton. Examine sea- 
cucumbers and compare, noting the difference in the relation 
between body axis in relation to normal position. Can you 
see the five rays? Tube feet? How would you homologize 
the outer surface of a sea-cucumber and a sea urchin? 
The sea cucumber and a starfish? The echinoderms 
are a very aberrant group. For a long time class- 
ed with the coelenterata because of their radial structure, 
they have since been clearly shown to be forms with far greater 
complexity of organization and are clearly animals which have 
been modified from bilaterally symmetrical ancestors possessing 
three germ-layers and a coelome. See demonstrations of the 
bilateral larval forms. Distinctive characters of the phylum 
are: a radial symmetry, masking a more fundamental bilateral 
symmetry, which appears in the larva; an extensive coelome; 
a water vascular system used for locomotion and unique in the 
animal kingdom; a skeleton consisting of isolated plates em- 



112 Classification. 

bedded in the mesoderm; a simple type of nervous system and 
sense organs. 

Phylum, Arthropoda. 

To this phylum belong the familiar crayfish, crabs, insects, 
spiders, scorpions, etc. Examine museum specimens of cray- 
fish and lobsters, if not already dissected, and compare with a 
crab, noting, mouth and anus, eyes, antennae, jointed appen- 
dages, external evidences of metamerism. In all these forms 
the relation of the nervous system to the gut is similar to that 
in the earthworm or crayfish. Examine water-fleas, as they 
swim in an aquarium and in a watch-glass after anaesthetizing 
with ether. In what respects do they agree with the larger 
forms in structure? Characteristic features of the phylum 
are: a continuous cuticular skeleton, thinner at the joints; 
bilateral symmetry; metamerism; a pair of jointed appendages 
on each segment; a pair of compound eyes; three germ layers. 
A well developed coelome is not present but it seems probable 
that such was the case in the ancestors of this group. 

Phylum, Chordata. 

The vertebrates constitute by far the most conspicuous 
members of this phylum and are sufficiently familiar without 
further examination in this connection. Other less known 
forms are the amphioxus and the tunicates or sea squirts. 
Examine specimens. The amphioxus with its elongated 
metameric body, mouth and anal openings and fins bears a 
remote resemblance to a fish. It can, at least, be imagined 
when viewed from the outside to have some resemblance to 
the simpler vertebrates. Internally there are gill-slits, a 
notochord, a dorsal tubular nervous system and other vertebrate 
characteristics. The sea-squirt, on the other hand, would 
never suggest such a relationship. It is adapted for a sessile 
life and possesses an inhalent and exhalent siphon much like 
those of a clam. Indeed these animals were for a long time 
classed with the mollusca. Later, it was shown that the 
embryo possessed the notochord, dorsal tubular nervous sys- 



Classification . 113 

tern and other features found in no other group but the verte- 
brates. Accordingly the tunicates were placed in a group 
with the vertebrates. Distinctive features of the 
chordata are: a dorsal tubular nervous system, formed by 
infolding as in the frog embryo; a notochord, present in embryo 
only (frog) or throughout life (amphioxus) ; metamerism more 
or less conspicuous; three germ layers; coelome; bilateral sym- 
metry, etc. 

II. PHYLOGENY OF THE ANIMAL KINGDOM 

(a) After this review of representative types we may next 
consider the grouping of the phyla into larger divisions. Here 
we must consider only a few very fundamental points of struc- 
ture such as, the many celled or single celled condition; with a 
gut cavity or without a gut cavity; diploblastic or triploblastic; 
with a coelome or without a coelome; with metamerism or 
without metamerism. 

Exercise 1. Construct a table showing how the phyla will 
group themselves when classified along broad lines. 

(b) Looked at in another way, this table will represent a 
family tree of the animal kingdom for it probably gives us 
the broad lines along which evolution has proceeded. Do you 
understand now the meaning of a natural classification or one 
based upon blood relationship and the meaning of structural 
resemblance among animals? 



114 Appendix. 



APPENDIX 

A BONY FISH 

Any of the common bony fish will serve for this study. The 
marine Ctenolabrus, fresh-water perch, or any of the minnows. 
They should be collected during the summer and preserved 
in formalin. Interest in the work is greatly increased by hav- 
ing a few live fish to study action of fins and manner of respi- 
ration. 

(a) External Characters. What is the shape of the body 
as a whole? How is it adapted for motion through the water? 
How do you distinguish anterior and posterior ends? Dorsal 
and ventral surface? Note the head, trunk and tail regions. 
Is there a neck? Are these regions sharply marked? What is 
the nature of the coverings of the body? 1. Head: Its 
shape? Mouth, nostrils, eyes, gill-openings, operculum, which 
consists of several parts. Beneath the operculum is the 
branchiostigal membrane, supported by bony rays. The 
branchiostigal region is connected with the trunk by the nar- 
row isthmus. Its shape? Relation to gill openings? 

(b) Trunk. Its general shape? How does this region 
compare as to length, height and thickness? Describe the 
color of your specimen? Compare several specimens, and 
male and female. Describe the variations noted. Note the 
lateral line on each side of the body. Can you trace it on the 
head? Determine what causes the line. 

(c) Fins. How many? How many in pairs? Single? 
What ones are in the median line of the body? How are they 
supported? The fin on the back is the dorsal. Are there one 
or two? Compare as to size and supporting rays. The ter- 
minal fin is the caudal, and the one just behind the vent is the 
anal. Compare each with the dorsal. Do the paired fins 
have supports? What is their position on the trunk? The 



A Bony Fish. 115 

anterior pair are the pectorals, the posterior the pelvic. Com- 
pare several kinds of fish and determine the variation in posi- 
tion of these fins. If practicable, the living fish should be 
studied in aquaria to determine the use of each fin. 

(d) Integument. Describe the distribution and arrange- 
ment of the scales. Is it regular? Do they extend into the 
head? Is there skin over the scales? Is the pigment in the 
scales? Pull one out. The rounded marginal scales are 
cycloid, the toothed or spiny marginal are the ctenoid. Sketch. 

(e) External Apertures. Determine the position, size and 
shape of the following: (a) mouth, (b) vent, (c) urino-geni- 
tal, (d) nostrils, (e) gill openings. 

(f) Mouth Cavity. Its general shape? Are there lips? 
The bony framework consists of the upper jaw, a pre-maxillary 
in front and a maxillary behind. Shape and size of each? 
The lower jaw is the dentary. Which ones bear teeth? Are 
there other bones that have teeth? Where? How many rows 
of teeth in jaw bones? Their shape and size? 1. Tongue: 
Shape? Attachment? Size? 2. Oesophagus: Position? 
3. Gills: Lift operculum and examine the gills. Each is 
composed of a bony arch and numerous gill filaments. On 
the inner edge of the bony arch are a number of short processes, 
the gill-rakers. How many gill-slits? Their relation to the 
pharynx? Are all the gills alike? Compare first and second 
and the last two. What use can you suggest for the gill- 
rakers? 

Exercise 1. Draw as seen from one side, showing the mouth 
and gill region dissected. 



116 A Snail. 



A POND SNAIL 

For the following study the French snail Helix will be found 
very satisfactory, but the common pond snails Physa, Plan- 
orbis or Limnea may be used to advantage. 

(a) The Shell. Is there any division into valves? What 
is its general form? How many turns does the shell make? 
How do they vary in size? Compare several specimens of the 
same species as well as several different species. Do the coils 
turn to the right, dextral, or to the left, sinistral? Is the coil- 
ing loose or close, flat or conical? The apex of the shell is 
the oldest part and corresponds to the umbo in the clam. 
The wide opening is the mouth or peristome (of the shell not 
the animal). What is its shape? Is the margin smooth or 
toothed? Explain. One side of the peristome is in some 
species drawn out into a spout-like process. What is its use? 
Do you find in any of the species an oval plate closing the 
opening? In some snails there is such a structure which is 
called the operculum. To what is it attached? Can you 
explain its use? The whorls make a line where they come in 
contact; this is the suture. Is the suture a simple or an 
irregular line? Explain the lines that run parallel to the edge 
of the peristome as lines of growth. Is there any variation? 
Explain. The whorls coil around a central axis, the columnella. 
Describe it in a demonstration specimen of some large shell, 
making a sketch to show its parts. 

(b) The Living Animal. How does the snail move? What 
is the shape of its foot? Its relation to the rest of the body? 
To the shell? The anterior region of the foot is termed the 
propodium; the posterior the metapodium; and between these 
two is the mesopodium. Are these regions sharply marked off? 
To which part is the operculum attached when present? 

(c) The Head Region. Dorsal to the foot find the mouth. 
Shape? On each side are fleshy tentacles. Their size and 
shape? Touch with needle. What happens? Are there one 



A Snail. 117 

or two pairs? Do you find small glistening spots, the eyes, 
on the tentacles? Their position? Locate the anal opening on 
the right side of the head. In the air breathing snails find the 
respiratory opening near the anal opening. 

Exercise 1. Draw from a side view, showing foot, head and 
shell as they appear when fully expanded. 

(d) The snail belongs to one of the sub-divisions of the 
Mollusca known as the Gastropoda. Explain the application 
of this term. From your study of the clam and snail, write 
a definition of the group Mollusca and the sub-group Gas- 
tropoda. 



OCT W ,913 



LIBRARY OF CONGRESS 



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